diff --git a/servermanager.py b/servermanager.py
index db06cfd..e1b2351 100644
--- a/servermanager.py
+++ b/servermanager.py
@@ -90,6 +90,8 @@ def server_command_builder(
     required_apoints: int = 0,
     cataclysm: int = 0,
 ):
+    available_nations = get_nations()
+
     if (not ((random_map == 0) ^ (mapfile == ""))) or random_map not in {0, 10, 15, 20}:
         return "ERROR_MAP"
 
@@ -120,6 +122,8 @@ def server_command_builder(
     if team_game:
         for team in teams:
             # TODO Check valid inputs
+            if team[0] not in available_nations[era]:
+                return "ERROR_INVALID_NATION"
             command.append(
                 " --team " + str(team[0]) + " " + str(team[1]) + " " + str(team[2])
             )