Annexationism

Annexationism is the desire to appropriate additional privileges, possessions or territories.^[1] Irredentism—reclaim and reoccupy a lost homeland—may be a subset of annexationism. The opposite of annexationism is separatism.

References

1. the OED defines the word only in terms of annexation: "advocacy of, or a policy aiming at, annexation". From annexation, sense c: esp[ecially] of attaching as an additional privilege, possession, or territorial dependency; appropriation".