diff --git a/backend/src/planetwars/mod.rs b/backend/src/planetwars/mod.rs
new file mode 100644
index 0000000..e69de29
diff --git a/backend/src/pw/mod.rs b/backend/src/pw/mod.rs
new file mode 100644
index 0000000..9e1ade5
--- /dev/null
+++ b/backend/src/pw/mod.rs
@@ -0,0 +1,11 @@
+
+pub mod pw_protocol;
+mod pw_controller;
+mod pw_rules;
+mod pw_config;
+mod pw_serializer;
+
+pub use self::pw_controller::PwMatch;
+pub use self::pw_rules::PlanetWars;
+pub use self::pw_config::Config;
+pub use self::pw_protocol::Map;
diff --git a/backend/src/pw/pw_config.rs b/backend/src/pw/pw_config.rs
new file mode 100644
index 0000000..694d0f4
--- /dev/null
+++ b/backend/src/pw/pw_config.rs
@@ -0,0 +1,79 @@
+use std::fs::File;
+use std::io::Read;
+use std::io;
+
+use serde_json;
+
+use super::pw_protocol as proto;
+use super::pw_rules::*;
+
+// TODO
+use server::ClientId;
+
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Config {
+    pub map_file: String,
+    pub max_turns: u64,
+}
+
+impl Config {
+    pub fn create_game(&self, clients: Vec<ClientId>) -> PlanetWars {
+        let planets = self.load_map(clients.len());
+        let players = clients.into_iter()
+            .map(|client_id| Player { id: client_id, alive: true })
+            .collect();
+
+        PlanetWars {
+            players: players,
+            planets: planets,
+            expeditions: Vec::new(),
+            expedition_num: 0,
+            turn_num: 0,
+            max_turns: self.max_turns,
+        }
+    }
+
+    fn load_map(&self, num_players: usize) -> Vec<Planet> {
+        let map = self.read_map().expect("[PLANET_WARS] reading map failed");
+
+        return map.planets
+            .into_iter()
+            .enumerate()
+            .map(|(num, planet)| {
+                let mut fleets = Vec::new();
+                let owner = planet.owner.and_then(|owner_num| {
+                    // in the current map format, player numbers start at 1.
+                    // TODO: we might want to change this.
+                    let player_num = owner_num as usize - 1;
+                    // ignore players that are not in the game
+                    if player_num < num_players {
+                        Some(player_num)
+                    } else {
+                        None
+                    }
+                });
+                if planet.ship_count > 0 {
+                    fleets.push(Fleet {
+                        owner: owner,
+                        ship_count: planet.ship_count,
+                    });
+                }
+                return Planet {
+                    id: num,
+                    name: planet.name,
+                    x: planet.x,
+                    y: planet.y,
+                    fleets: fleets,
+                };
+            }).collect();
+    }
+
+    fn read_map(&self) -> io::Result<proto::Map> {
+        let mut file = File::open(&self.map_file)?;
+        let mut buf = String::new();
+        file.read_to_string(&mut buf)?;
+        let map = serde_json::from_str(&buf)?;
+        return Ok(map);
+    }
+}
diff --git a/backend/src/pw/pw_controller.rs b/backend/src/pw/pw_controller.rs
new file mode 100644
index 0000000..1a7ac5f
--- /dev/null
+++ b/backend/src/pw/pw_controller.rs
@@ -0,0 +1,452 @@
+use std::collections::{HashMap, HashSet};
+use std::time::{Duration, Instant};
+use std::mem;
+use std::io;
+
+use events;
+use network::server::RegisteredHandle;
+use reactors::reactor::ReactorHandle;
+use reactors::{WireEvent, RequestHandler};
+use server::{ClientId, ConnectionManager};
+use sodiumoxide::crypto::sign::PublicKey;
+
+use super::Config;
+use super::pw_rules::{PlanetWars, Dispatch};
+use super::pw_serializer::serialize_state;
+use super::pw_protocol::{
+    self as proto,
+    PlayerAction,
+    PlayerCommand, 
+    CommandError,
+};
+
+use serde_json;
+
+pub struct Player {
+    id: ClientId,
+    num: usize,
+    handle: RegisteredHandle,
+}
+
+pub struct ClientHandler {
+    client_id: u32,
+    reactor_handle: ReactorHandle,
+}
+
+impl ClientHandler {
+    pub fn new(client_id: u32, reactor_handle: ReactorHandle) -> Self {
+        ClientHandler {
+            client_id,
+            reactor_handle,
+        }
+    }
+
+    pub fn on_connect(&mut self, _event: &events::Connected)
+        -> io::Result<WireEvent>
+    {
+        self.reactor_handle.dispatch(events::ClientConnected {
+            client_id: self.client_id,
+        });
+        Ok(WireEvent::null())
+    }
+
+    pub fn on_disconnect(&mut self, _event: &events::Disconnected)
+        -> io::Result<WireEvent>
+    {
+        self.reactor_handle.dispatch(events::ClientDisconnected {
+            client_id: self.client_id,
+        });
+        Ok(WireEvent::null())
+    }
+
+    pub fn on_message(&mut self, event: &events::ClientSend)
+        -> io::Result<WireEvent>
+    {
+        self.reactor_handle.dispatch(events::ClientMessage {
+            client_id: self.client_id,
+            data: event.data.clone(),
+        });
+        Ok(WireEvent::null())
+    }
+}
+
+pub struct PwMatch {
+    state: PwMatchState,
+}
+
+enum PwMatchState {
+    Lobby(Lobby),
+    Playing(PwController),
+    Finished,
+}
+
+impl PwMatch {
+    pub fn new(match_uuid: Vec<u8>,
+               reactor_handle: ReactorHandle,
+               connection_manager: ConnectionManager)
+               -> Self
+    {
+        let lobby = Lobby::new(
+            match_uuid,
+            connection_manager,
+            reactor_handle
+        );
+
+        return PwMatch {
+            state: PwMatchState::Lobby(lobby),
+        }
+    }
+
+    fn take_state(&mut self) -> PwMatchState {
+        mem::replace(&mut self.state, PwMatchState::Finished)
+    }
+
+    pub fn register_client(&mut self, event: &events::RegisterClient) {
+        if let &mut PwMatchState::Lobby(ref mut lobby) = &mut self.state {
+            let client_id = ClientId::new(event.client_id);
+            let key = PublicKey::from_slice(&event.public_key).unwrap();
+            lobby.add_player(client_id, key);
+        }
+    }
+
+    pub fn remove_client(&mut self, event: &events::RemoveClient) {
+        if let PwMatchState::Lobby(ref mut lobby) = self.state {
+            let client_id = ClientId::new(event.client_id);
+            lobby.remove_player(client_id);
+        }
+    }
+
+    pub fn start_game(&mut self, event: &events::StartGame) {
+        let state = self.take_state();
+
+        if let PwMatchState::Lobby(lobby) = state {
+            let config = Config {
+                map_file: event.map_path.clone(),
+                max_turns: event.max_turns as u64,
+            };
+            self.state = PwMatchState::Playing(PwController::new(
+                config,
+                lobby.reactor_handle,
+                lobby.connection_manager,
+                lobby.players,
+            ));
+        } else {
+            self.state = state;
+        }
+    }
+
+    pub fn game_step(&mut self, event: &events::GameStep) {
+        if let PwMatchState::Playing(ref mut controller) = self.state {
+            controller.on_step(event);
+        }
+    }
+
+    pub fn client_message(&mut self, event: &events::ClientMessage) {
+        if let PwMatchState::Playing(ref mut controller) = self.state {
+            controller.on_client_message(event);
+        }
+    }
+
+    pub fn game_finished(&mut self, event: &events::GameFinished) {
+        let state = self.take_state();
+        if let PwMatchState::Playing(mut controller) = state {
+            controller.on_finished(event);
+        }
+        self.state = PwMatchState::Finished;
+    }
+
+    pub fn timeout(&mut self, event: &events::TurnTimeout) {
+        if let PwMatchState::Playing(ref mut controller) = self.state {
+            controller.on_timeout(event);
+        }
+    }
+}
+
+pub struct Lobby {
+    match_uuid: Vec<u8>,
+    connection_manager: ConnectionManager,
+    reactor_handle: ReactorHandle,
+
+    players: HashMap<ClientId, RegisteredHandle>,
+}
+
+impl Lobby {
+    fn new(match_uuid: Vec<u8>,
+           connection_manager: ConnectionManager,
+           reactor_handle: ReactorHandle)
+           -> Self
+    {
+        return Lobby {
+            match_uuid,
+            connection_manager,
+            reactor_handle,
+
+            players: HashMap::new(),
+            // start counter at 1, because 0 is the control client
+        }
+    }
+
+    fn add_player(&mut self, client_id: ClientId, public_key: PublicKey) {
+        let mut core = RequestHandler::new(
+            ClientHandler::new(
+                client_id.as_u32(),
+                self.reactor_handle.clone(),
+            ),
+        );
+
+        core.add_handler(ClientHandler::on_connect);
+        core.add_handler(ClientHandler::on_disconnect);
+        core.add_handler(ClientHandler::on_message);
+
+        let handle = self.connection_manager.create_client(
+            self.match_uuid.clone(),
+            client_id.as_u32(),
+            public_key,
+            core
+        );
+
+        self.players.insert(client_id, handle);
+    }
+
+    fn remove_player(&mut self, client_id: ClientId) {
+        self.players.remove(&client_id);
+    }
+}
+
+pub struct PwController {
+    state: PlanetWars,
+    planet_map: HashMap<String, usize>,
+    reactor_handle: ReactorHandle,
+    connection_manager: ConnectionManager,
+
+    client_player: HashMap<ClientId, usize>,
+    players: HashMap<ClientId, Player>,
+
+    waiting_for: HashSet<ClientId>,
+    commands: HashMap<ClientId, String>,
+}
+
+impl PwController {
+    pub fn new(config: Config,
+               reactor_handle: ReactorHandle,
+               connection_manager: ConnectionManager,
+               clients: HashMap<ClientId, RegisteredHandle>)
+        -> Self
+    {
+        // TODO: we probably want a way to fixate player order
+        let client_ids = clients.keys().cloned().collect();
+        let state = config.create_game(client_ids);
+
+        let planet_map = state.planets.iter().map(|planet| {
+            (planet.name.clone(), planet.id)
+        }).collect();
+
+        let mut client_player = HashMap::new();
+        let mut players = HashMap::new();
+
+        let clients_iter = clients.into_iter().enumerate();
+        for (player_num, (client_id, client_handle)) in clients_iter {
+            client_player.insert(client_id, player_num);
+            players.insert(client_id, Player {
+                id: client_id,
+                num: player_num,
+                handle: client_handle,
+            });
+        }
+
+        let mut controller = PwController {
+            state,
+            planet_map,
+            players,
+            client_player,
+            reactor_handle,
+            connection_manager,
+
+            waiting_for: HashSet::new(),
+            commands: HashMap::new(),
+        };
+        // this initial dispatch starts the game
+        controller.dispatch_state();
+        return controller;
+    }
+
+
+    /// Advance the game by one turn.
+    fn step(&mut self) {
+        self.state.repopulate();
+        self.execute_commands();
+        self.state.step();
+
+        self.dispatch_state();
+    }
+
+    fn dispatch_state(&mut self) {
+        let turn_num = self.state.turn_num;
+        // TODO: fix this
+        let state = serde_json::to_string(&serialize_state(&self.state)).unwrap();
+
+        if self.state.is_finished() {
+            let event = events::GameFinished { turn_num, state };
+            self.reactor_handle.dispatch(event);
+        } else {
+            let event = events::GameStep { turn_num, state };
+            self.reactor_handle.dispatch(event);
+        }
+    }
+
+    fn on_step(&mut self, step: &events::GameStep) {
+        let state = &self.state;
+        let waiting_for = &mut self.waiting_for;
+
+        self.players.retain(|_, player| {
+            if state.players[player.num].alive {
+                waiting_for.insert(player.id);
+                player.handle.dispatch(events::GameStep {
+                    turn_num: step.turn_num,
+                    state: step.state.clone(),
+                });
+                // keep this player in the game
+                return true;
+            } else {
+                player.handle.dispatch(events::GameFinished {
+                    turn_num: step.turn_num,
+                    state: step.state.clone(),
+                });
+                // this player is dead, kick him!
+                // TODO: shutdown the reactor
+                // TODO: todo
+                return false;
+            }
+        });
+
+        let deadline = Instant::now() + Duration::from_secs(1);
+        self.reactor_handle.dispatch_at(deadline, events::TurnTimeout {
+            turn_num: state.turn_num,
+        });
+    }
+
+    fn on_client_message(&mut self, event: &events::ClientMessage) {
+        let client_id = ClientId::new(event.client_id);
+        self.waiting_for.remove(&client_id);
+        self.commands.insert(client_id, event.data.clone());
+
+        if self.waiting_for.is_empty() {
+            self.step();
+        }
+    }
+
+    fn on_finished(&mut self, event: &events::GameFinished) {
+        self.players.retain(|_player_id, player| {
+            player.handle.dispatch(events::GameFinished {
+                turn_num: event.turn_num,
+                state: event.state.clone(),
+            });
+            // game is over, kick everyone.
+            false
+        });
+        println!("everybody has been kicked");
+        self.reactor_handle.quit();
+    }
+
+    fn on_timeout(&mut self, event: &events::TurnTimeout) {
+        if self.state.turn_num == event.turn_num {
+            self.step();
+        }
+    }
+
+    fn player_commands(&mut self) -> HashMap<ClientId, Option<String>> {
+        let commands = &mut self.commands;
+        return self.players.values().map(|player| {
+            let command = commands.remove(&player.id);
+            return (player.id, command);
+        }).collect();
+    }
+
+    fn execute_commands(&mut self) {
+        let mut commands = self.player_commands();
+
+        for (player_id, command) in commands.drain() {
+            let player_num = self.players[&player_id].num;
+            let action = self.execute_action(player_num, command);
+            let serialized_action = serde_json::to_string(&action).unwrap();
+            self.reactor_handle.dispatch(events::PlayerAction {
+                client_id: player_id.as_u32(),
+                action: serialized_action.clone(),
+            });
+            self.players
+                .get_mut(&player_id)
+                .unwrap()
+                .handle
+                .dispatch(events::PlayerAction {
+                    client_id: player_id.as_u32(),
+                    action: serialized_action,
+                });
+        }
+    }
+
+    fn execute_action(&mut self, player_num: usize, response: Option<String>)
+        -> PlayerAction
+    {
+        // TODO: it would be cool if this could be done with error_chain.
+
+        let message = match response {
+            None => return PlayerAction::Timeout,
+            Some(message) => message,
+        };
+
+        let action: proto::Action = match serde_json::from_str(&message) {
+            Err(err) => return PlayerAction::ParseError(err.to_string()),
+            Ok(action) => action,
+        };
+
+        let commands = action.commands.into_iter().map(|command| {
+            match self.parse_command(player_num, &command) {
+                Ok(dispatch) => {
+                    self.state.dispatch(&dispatch);
+                    PlayerCommand {
+                        command,
+                        error: None,
+                    }
+                },
+                Err(error) => {
+                    PlayerCommand {
+                        command,
+                        error: Some(error),
+                    }
+                }
+            }
+        }).collect();
+
+        return PlayerAction::Commands(commands);
+    }
+
+    fn parse_command(&self, player_num: usize, mv: &proto::Command)
+                     -> Result<Dispatch, CommandError>
+    {
+        let origin_id = *self.planet_map
+            .get(&mv.origin)
+            .ok_or(CommandError::OriginDoesNotExist)?;
+
+        let target_id = *self.planet_map
+            .get(&mv.destination)
+            .ok_or(CommandError::DestinationDoesNotExist)?;
+
+        if self.state.planets[origin_id].owner() != Some(player_num) {
+            return Err(CommandError::OriginNotOwned);
+        }
+
+        if self.state.planets[origin_id].ship_count() < mv.ship_count {
+            return Err(CommandError::NotEnoughShips);
+        }
+
+        if mv.ship_count == 0 {
+            return Err(CommandError::ZeroShipMove);
+        }
+
+        Ok(Dispatch {
+            origin: origin_id,
+            target: target_id,
+            ship_count: mv.ship_count,
+        })
+    }
+}
\ No newline at end of file
diff --git a/backend/src/pw/pw_protocol.rs b/backend/src/pw/pw_protocol.rs
new file mode 100644
index 0000000..9eb5c1c
--- /dev/null
+++ b/backend/src/pw/pw_protocol.rs
@@ -0,0 +1,105 @@
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Expedition {
+    pub id: u64,
+    pub ship_count: u64,
+    pub origin: String,
+    pub destination: String,
+    pub owner: u32,
+    pub turns_remaining: u64,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Planet {
+    pub ship_count: u64,
+    pub x: f64,
+    pub y: f64,
+    pub owner: Option<u32>,
+    pub name: String,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Action {
+    #[serde(rename = "moves")]
+    pub commands: Vec<Command>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Command {
+    pub origin: String,
+    pub destination: String,
+    pub ship_count: u64,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Map {
+    pub planets: Vec<Planet>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct State {
+    pub planets: Vec<Planet>,
+    pub expeditions: Vec<Expedition>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct GameInfo {
+    pub players: Vec<String>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub enum CommandError {
+    NotEnoughShips,
+    OriginNotOwned,
+    ZeroShipMove,
+    OriginDoesNotExist,
+    DestinationDoesNotExist,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct PlayerCommand {
+    pub command: Command,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub error: Option<CommandError>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+#[serde(tag = "type", content = "value")]
+pub enum PlayerAction {
+    Timeout,
+    ParseError(String),
+    Commands(Vec<PlayerCommand>),
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+#[serde(tag = "type", content = "content")]
+pub enum ServerMessage {
+    /// Game state in current turn
+    GameState(State),
+    /// The action that was performed
+    PlayerAction(PlayerAction),
+    /// The game is over, and this is the concluding state.
+    FinalState(State),
+}
+
+// lobby messages
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+#[serde(tag = "type", content = "content")]
+pub enum ControlMessage {
+    PlayerConnected {
+        player_id: u64,
+    },
+    PlayerDisconnected {
+        player_id: u64,
+    },
+    GameState(State),
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+#[serde(tag = "type", content = "content")]
+pub enum LobbyCommand {
+    StartMatch,
+}
diff --git a/backend/src/pw/pw_rules.rs b/backend/src/pw/pw_rules.rs
new file mode 100644
index 0000000..ed66b26
--- /dev/null
+++ b/backend/src/pw/pw_rules.rs
@@ -0,0 +1,200 @@
+use server::ClientId;
+
+/// The planet wars game rules.
+pub struct PlanetWars {
+    pub players: Vec<Player>,
+    pub planets: Vec<Planet>,
+    pub expeditions: Vec<Expedition>,
+    // How many expeditions were already dispatched.
+    // This is needed for assigning expedition identifiers.
+    pub expedition_num: u64,
+    pub turn_num: u64,
+    pub max_turns: u64,
+}
+
+#[derive(Debug)]
+pub struct Player {
+    pub id: ClientId,
+    pub alive: bool,
+}
+
+#[derive(Debug)]
+pub struct Fleet {
+    pub owner: Option<usize>,
+    pub ship_count: u64,
+}
+
+#[derive(Debug)]
+pub struct Planet {
+    pub id: usize,
+    pub name: String,
+    pub fleets: Vec<Fleet>,
+    pub x: f64,
+    pub y: f64,
+}
+
+#[derive(Debug)]
+pub struct Expedition {
+    pub id: u64,
+    pub origin: usize,
+    pub target: usize,
+    pub fleet: Fleet,
+    pub turns_remaining: u64,
+}
+
+#[derive(Debug)]
+pub struct Dispatch {
+    pub origin: usize,
+    pub target: usize,
+    pub ship_count: u64,
+}
+
+impl PlanetWars {
+
+    pub fn dispatch(&mut self, dispatch: &Dispatch) {
+        let distance = self.planets[dispatch.origin].distance(
+            &self.planets[dispatch.target]
+        );
+
+        let origin = &mut self.planets[dispatch.origin];
+        origin.fleets[0].ship_count -= dispatch.ship_count;
+
+
+        let expedition = Expedition {
+            id: self.expedition_num,
+            origin: dispatch.origin,
+            target: dispatch.target,
+            turns_remaining: distance,
+            fleet: Fleet {
+                owner: origin.owner(),
+                ship_count: dispatch.ship_count,
+            },
+        };
+
+        // increment counter
+        self.expedition_num += 1;
+        self.expeditions.push(expedition);
+    }
+
+    // Play one step of the game
+    pub fn step(&mut self) {
+        self.turn_num += 1;
+
+        // Initially mark all players dead, re-marking them as alive once we
+        // encounter a sign of life.
+        for player in self.players.iter_mut() {
+            player.alive = false;
+        }
+
+        self.step_expeditions();
+        self.resolve_combat();
+    }
+
+    pub fn repopulate(&mut self) {
+        for planet in self.planets.iter_mut() {
+            if planet.owner().is_some() {
+                planet.fleets[0].ship_count += 1;
+            }
+        }
+    }
+
+    fn step_expeditions(&mut self) {
+        let mut i = 0;
+        let exps = &mut self.expeditions;
+        while i < exps.len() {
+            // compare with 1 to avoid issues with planet distance 0
+            if exps[i].turns_remaining <= 1 {
+                // remove expedition from expeditions, and add to fleet
+                let exp = exps.swap_remove(i);
+                let planet = &mut self.planets[exp.target];
+                planet.orbit(exp.fleet);
+            } else {
+                exps[i].turns_remaining -= 1;
+                if let Some(owner_num) = exps[i].fleet.owner {
+                    // owner has an expedition in progress; this is a sign of life.
+                    self.players[owner_num].alive = true;
+                }
+
+                // proceed to next expedition
+                i += 1;
+            }
+        }
+    }
+
+    fn resolve_combat(&mut self) {
+        for planet in self.planets.iter_mut() {
+            planet.resolve_combat();
+            if let Some(owner_num) = planet.owner() {
+                // owner owns a planet; this is a sign of life.
+                self.players[owner_num].alive = true;
+            }
+        }
+    }
+
+    pub fn is_finished(&self) -> bool {
+        let remaining = self.players.iter().filter(|p| p.alive).count();
+        return remaining < 2 || self.turn_num >= self.max_turns;
+    }
+
+    pub fn living_players(&self) -> Vec<ClientId> {
+        self.players.iter().filter_map(|p| {
+            if p.alive {
+                Some(p.id)
+            } else {
+                None
+            }
+        }).collect()
+    }
+}
+
+
+impl Planet {
+    pub fn owner(&self) -> Option<usize> {
+        self.fleets.first().and_then(|f| f.owner)
+    }
+
+    pub fn ship_count(&self) -> u64 {
+        self.fleets.first().map_or(0, |f| f.ship_count)
+    }
+
+    /// Make a fleet orbit this planet.
+    fn orbit(&mut self, fleet: Fleet) {
+        // If owner already has a fleet present, merge
+        for other in self.fleets.iter_mut() {
+            if other.owner == fleet.owner {
+                other.ship_count += fleet.ship_count;
+                return;
+            }
+        }
+        // else, add fleet to fleets list
+        self.fleets.push(fleet);
+    }
+
+    fn resolve_combat(&mut self) {
+        // The player owning the largest fleet present will win the combat.
+        // Here, we resolve how many ships he will have left.
+        // note: in the current implementation, we could resolve by doing
+        // winner.ship_count -= second_largest.ship_count, but this does not
+        // allow for simple customizations (such as changing combat balance).
+
+        self.fleets.sort_by(|a, b| a.ship_count.cmp(&b.ship_count).reverse());
+        while self.fleets.len() > 1 {
+            let fleet = self.fleets.pop().unwrap();
+            // destroy some ships
+            for other in self.fleets.iter_mut() {
+                other.ship_count -= fleet.ship_count;
+            }
+
+            // remove dead fleets
+            while self.fleets.last().map(|f| f.ship_count) == Some(0) {
+                self.fleets.pop();
+            }
+        }
+    }
+
+    fn distance(&self, other: &Planet) -> u64 {
+        let dx = self.x - other.x;
+        let dy = self.y - other.y;
+        return (dx.powi(2) + dy.powi(2)).sqrt().ceil() as u64;
+    }
+}
\ No newline at end of file
diff --git a/backend/src/pw/pw_serializer.rs b/backend/src/pw/pw_serializer.rs
new file mode 100644
index 0000000..c258f7e
--- /dev/null
+++ b/backend/src/pw/pw_serializer.rs
@@ -0,0 +1,61 @@
+use super::pw_rules::{PlanetWars, Planet, Expedition};
+use super::pw_protocol as proto;
+
+/// Serialize given gamestate
+pub fn serialize_state(state: &PlanetWars) -> proto::State {
+    let serializer = Serializer::new(state);
+    serializer.serialize_state()
+}
+
+struct Serializer<'a> {
+    state: &'a PlanetWars,
+}
+
+impl<'a> Serializer<'a> {
+    fn new(state: &'a PlanetWars) -> Self {
+        Serializer {
+            state: state,
+        }
+    }
+
+    fn serialize_state(&self) -> proto::State {
+        proto::State {
+            planets: self.state
+                .planets
+                .iter()
+                .map(|planet| self.serialize_planet(planet))
+                .collect(),
+            expeditions: self.state
+                .expeditions
+                .iter()
+                .map(|exp| self.serialize_expedition(exp))
+                .collect(),
+        }
+    }
+
+    // gets the client id for a player number
+    fn player_client_id(&self, player_num: usize) -> u32 {
+        self.state.players[player_num].id.as_u32()
+    }
+
+    fn serialize_planet(&self, planet: &Planet) -> proto::Planet {
+        proto::Planet {
+            name: planet.name.clone(),
+            x: planet.x,
+            y: planet.y,
+            owner: planet.owner().map(|num| self.player_client_id(num)),
+            ship_count: planet.ship_count(),
+        }
+    }
+
+    fn serialize_expedition(&self, exp: &Expedition) -> proto::Expedition {
+        proto::Expedition {
+            id: exp.id,
+            owner: self.player_client_id(exp.fleet.owner.unwrap()),
+            ship_count: exp.fleet.ship_count,
+            origin: self.state.planets[exp.origin].name.clone(),
+            destination: self.state.planets[exp.target].name.clone(),
+            turns_remaining: exp.turns_remaining,
+        }
+    }
+}