diff --git a/aoe/dependencies.py b/aoe/dependencies.py
index 8d9b843..abdee3c 100644
--- a/aoe/dependencies.py
+++ b/aoe/dependencies.py
@@ -1,9 +1,77 @@
 from aoe.types import *
+from aoe.exceptions import *
 
 
 
-class BuildingDependencies():
+class Dependencies():
+
+
+    def check_dependencies(self, world, thing):
+        if type(thing) == Ages:
+            self._check_age_dependencies(world, thing)
+        else:
+            self._check_non_age_dependencies(world, thing)
+
+
+    def _check_non_age_dependencies(self, world, thing):
+        for dep in self.dependencies[thing]:
+            if dep not in world.buildings and \
+                    dep not in world.research and \
+                    not self._is_sufficient_age(world, dep):
+                        raise MissingDependencyException
+
+
+    @staticmethod
+    def _is_sufficient_age(world, age):
+        if type(age) == Ages and world.age >= age:
+            return True
+        return False
+
+
+    def _check_age_dependencies(self, world, age):
+        total_buildings = 0
+        for building in self.age_dependencies[age].keys():
+            if world.has_building(building):
+                total_buildings += self.age_dependencies[age][building]
+        if total_buildings < self.age_dependencies_counts[age]:
+            raise MissingDependencyException
+
+
     def __init__(self):
+        self.age_dependencies = {
+                             Ages.FEUDAL: {
+                                           Buildings.BARRACKS: 1,
+                                           Buildings.MILL: 1,
+                                           Buildings.LUMBERCAMP: 1,
+                                           Buildings.MININGCAMP: 1,
+                                           Buildings.DOCK: 1,
+                                           #Buildings.MULECART: 1,
+                                           #Buildings.FOLWARK: 1,
+                                           #Buildings.SETTLEMENT: 2,
+                                          },
+                             Ages.CASTLE: {
+                                           Buildings.ARCHERYRANGE: 1,
+                                           Buildings.STABLE: 1,
+                                           Buildings.MARKET: 1,
+                                           Buildings.BLACKSMITH: 1,
+                                           #Buildings.SIEGEWORKSHOP: 1,
+                                          },
+                             Ages.IMPERIAL: {
+                                             #Buildings.MONASTERY: 1,
+                                             #Buildings.FORTIFIEDCHURCH: 1,
+                                             #Buildings.UNIVERSITY: 1,
+                                             #Buildings.SIEGEWORKSHOP: 1,
+                                             #Buildings.CASTLE: 2,
+                                             #Buildings.KREPOST: 2,
+                                            },
+                             }
+
+        self.age_dependencies_counts = {
+                                    Ages.FEUDAL: 2,
+                                    Ages.CASTLE: 2,
+                                    Ages.IMPERIAL: 2,
+                                   }
+
         self.dependencies = {
                              Buildings.HOUSE: [Ages.DARK],
                              Buildings.LUMBERCAMP: [Ages.DARK],
@@ -39,50 +107,6 @@ class BuildingDependencies():
                              #Buildings.FEITORIA: [Ages.IMPERIAL],
                              Buildings.BOMBARDTOWER: [Ages.IMPERIAL, Research.BOMBARDTOWER],
                              Buildings.WONDER: [Ages.IMPERIAL],
-                            }
-
-
-
-class AgeDependencies():
-    def __init__(self):
-        self.dependencies = {
-                             Ages.FEUDAL: {
-                                           Buildings.BARRACKS: 1,
-                                           Buildings.MILL: 1,
-                                           Buildings.LUMBERCAMP: 1,
-                                           Buildings.MININGCAMP: 1,
-                                           Buildings.DOCK: 1,
-                                           #Buildings.MULECART: 1,
-                                           #Buildings.FOLWARK: 1,
-                                           #Buildings.SETTLEMENT: 2,
-                                          },
-                             Ages.CASTLE: {
-                                           Buildings.ARCHERYRANGE: 1,
-                                           Buildings.STABLE: 1,
-                                           Buildings.MARKET: 1,
-                                           Buildings.BLACKSMITH: 1,
-                                           #Buildings.SIEGEWORKSHOP: 1,
-                                          },
-                             Ages.IMPERIAL: {
-                                             #Buildings.MONASTERY: 1,
-                                             #Buildings.FORTIFIEDCHURCH: 1,
-                                             #Buildings.UNIVERSITY: 1,
-                                             #Buildings.SIEGEWORKSHOP: 1,
-                                             #Buildings.CASTLE: 2,
-                                             #Buildings.KREPOST: 2,
-                                            },
-                             }
-        self.dependencies_counts = {
-                                    Ages.FEUDAL: 2,
-                                    Ages.CASTLE: 2,
-                                    Ages.IMPERIAL: 2,
-                                   }
-
-
-
-class ResearchDependencies():
-    def __init__(self):
-        self.dependencies = {
                              Research.TOWNWATCH: [Ages.FEUDAL,
                                                   Buildings.TOWNCENTER],
                              Research.TOWNPATROL: [Ages.CASTLE,
@@ -237,13 +261,6 @@ class ResearchDependencies():
                              Research.BOMBARDTOWER: [Ages.IMPERIAL,
                                                      Buildings.UNIVERSITY,
                                                      Research.CHEMISTRY],
-                            }
-
-
-
-class UnitDependencies():
-    def __init__(self):
-        self.dependencies = {
                              Units.VILLAGER: [Buildings.TOWNCENTER],
                              Units.TRADECART: [Buildings.MARKET],
                              Units.SPEARMAN: [Ages.FEUDAL, Buildings.BARRACKS],
diff --git a/aoe/world.py b/aoe/world.py
index 37a0f1f..7ab9a9f 100644
--- a/aoe/world.py
+++ b/aoe/world.py
@@ -69,44 +69,6 @@ class World():
             self.resources[i] -= self.costs.costs[purchase][i]
 
 
-    def _check_dependencies(self, thing):
-        thing_type = type(thing)
-
-        if thing_type == Ages:
-            self._check_age_dependencies(thing)
-        else:
-            if thing_type == Buildings:
-                dependencies = self.building_deps.dependencies[thing]
-            elif thing_type == Units:
-                dependencies = self.unit_deps.dependencies[thing]
-            elif thing_type == Research:
-                dependencies = self.research_deps.dependencies[thing]
-            self._check_non_age_dependencies(dependencies)
-
-
-    def _check_non_age_dependencies(self, dependencies):
-        for dep in dependencies:
-            if dep not in self.buildings and \
-                    dep not in self.research and \
-                    not self._is_sufficient_age(dep):
-                        raise MissingDependencyException
-
-
-    def _is_sufficient_age(self, age):
-        if type(age) == Ages and self.age >= age:
-            return True
-        return False
-
-
-    def _check_age_dependencies(self, age):
-        total_buildings = 0
-        for building in self.age_deps.dependencies[age].keys():
-            if self.has_building(building):
-                total_buildings += self.age_deps.dependencies[age][building]
-        if total_buildings < self.age_deps.dependencies_counts[age]:
-            raise MissingDependencyException
-
-
     def _schedule_next_gather_rate_decrease(self, task):
         if task in [Tasks.IDLE, Tasks.BUILD]:
             return
@@ -252,7 +214,7 @@ class World():
 
         self._check_villager_move(villagers_from_count)
 
-        self._check_dependencies(building)
+        self.dependencies.check_dependencies(self, building)
 
         self._pay_cost(building)
         self._move_villagers_to_build(villagers_from_count)
@@ -458,7 +420,7 @@ class World():
 
 
     def _queue_thing(self, thing, initial_task=None):
-        self._check_dependencies(thing)
+        self.dependencies.check_dependencies(self, thing)
         self._pay_cost(thing)
 
         self._start_producing(thing, initial_task)
@@ -538,10 +500,7 @@ class World():
 
         self.build_times = Times()
         self.costs = Costs()
-        self.building_deps = BuildingDependencies()
-        self.age_deps = AgeDependencies()
-        self.research_deps = ResearchDependencies()
-        self.unit_deps = UnitDependencies()
+        self.dependencies = Dependencies()
         self.housing = Housing()
         self.production = Production()
         self.gather = Gather()