diff --git a/crates/bevy_app/src/app.rs b/crates/bevy_app/src/app.rs
index c159355ce8801..1dee75edb9e5b 100644
--- a/crates/bevy_app/src/app.rs
+++ b/crates/bevy_app/src/app.rs
@@ -360,66 +360,6 @@ impl App {
         self
     }
 
-    /// Sets up a state `S: States` that will only exist when the `Parent: States` state's matches
-    /// the provided condition. Creates an instance of [`apply_state_transition::<S>`] in
-    /// [`StateTransition`] so that transitions happen before [`Update`](crate::Update), as
-    /// well as instances of [`initialize_state_and_enter::<S>`] and [`remove_state_from_world::<S>`]
-    /// to set up and run [`OnEnter`] and [`OnExit`] schedules for `S` when appropriate.
-    ///
-    /// Whenever the parent enters a matching state, `S` will be set to `S::default()`.
-    ///
-    /// In addition, adds an instance of [`apply_state_transition::<S>`] in
-    /// [`StateTransition`] so that transitions happen before [`Update`](crate::Update).
-    ///
-    /// You can treat these just like any other states, but bear in mind that the `State<S>` and `NextState<S>`
-    /// resources might not exist.
-    pub fn add_sub_state<S: States, Parent: States>(
-        &mut self,
-        condition: impl StateMatcher<Parent>,
-    ) -> &mut Self {
-        self.add_systems(
-            Parent::on_enter_matching(condition.clone()),
-            initialize_state_and_enter::<S>,
-        )
-        .add_systems(
-            Parent::on_exit_matching(condition.clone()),
-            remove_state_from_world::<S>,
-        )
-        .add_systems(
-            StateTransition,
-            apply_state_transition::<S>.run_if(in_state(condition)),
-        );
-
-        self
-    }
-
-    /// Adds a [`State<S>`] and [`NextState<S>`] whenever entering a matching `Parent` state
-    /// regardless of whether the previous `Parent` state matches, and runs OnEnter/OnExit when those occur.
-    ///
-    /// In addition, adds an instance of [`apply_state_transition::<S>`] in
-    /// [`StateTransition`] so that transitions happen before [`Update`](crate::Update).
-    ///
-    /// You can treat these just like any other states, but bear in mind that the `State<S>` and `NextState<S>`
-    /// resources might not exist.
-    pub fn add_strict_sub_state<S: States, Parent: States>(
-        &mut self,
-        condition: impl StateMatcher<Parent>,
-    ) -> &mut Self {
-        self.add_systems(
-            Parent::on_enter_matching_strict(condition.clone()),
-            initialize_state_and_enter::<S>,
-        )
-        .add_systems(
-            Parent::on_enter_matching_strict(condition.clone()),
-            remove_state_from_world::<S>,
-        )
-        .add_systems(
-            StateTransition,
-            apply_state_transition::<S>.run_if(in_state(condition)),
-        );
-        self
-    }
-
     /// Adds a system to the given schedule in this app's [`Schedules`].
     ///
     /// # Examples
diff --git a/crates/bevy_ecs/src/schedule/state.rs b/crates/bevy_ecs/src/schedule/state.rs
index 0b70cb21ce8c6..5ef50d1e37d8a 100644
--- a/crates/bevy_ecs/src/schedule/state.rs
+++ b/crates/bevy_ecs/src/schedule/state.rs
@@ -464,44 +464,6 @@ impl<S: States> NextState<S> {
     }
 }
 
-/// If the state doesn't exist, initializes it to default runs `OnEnter`
-pub fn initialize_state_and_enter<S: States>(world: &mut World) {
-    world.insert_resource(NextState::<S>::Keep);
-
-    if world.contains_resource::<State<S>>() {
-        return;
-    }
-
-    let default = S::default();
-
-    world.insert_resource(State(default.clone()));
-
-    world.try_run_schedule(OnEnter(default)).ok();
-    world
-        .try_run_schedule(OnStateEntry::<S>(PhantomData::<S>))
-        .ok();
-}
-
-/// If the state exists, removes it and runs `OnExit`
-pub fn remove_state_from_world<S: States>(world: &mut World) {
-    world.remove_resource::<NextState<S>>();
-
-    let Some(state) = world.get_resource::<State<S>>() else {
-        return;
-    };
-    let state = state.0.clone();
-
-    world.remove_resource::<State<S>>();
-
-    world.insert_resource(PreviousState(state.clone()));
-
-    world.try_run_schedule(OnExit(state)).ok();
-    world
-        .try_run_schedule(OnStateExit::<S>(PhantomData::<S>))
-        .ok();
-    world.remove_resource::<PreviousState<S>>();
-}
-
 /// Run the enter schedule (if it exists) for the current state.
 pub fn run_enter_schedule<S: States>(world: &mut World) {
     let Some(state) = world.get_resource::<State<S>>().map(|s| s.0.clone()) else {