Joint sovereignty exercised over country by two or more countries

One word substitute is Condominium.

Colonialism: the policy or practice of acquiring full or partial political control over another country, occupying it with settlers, and exploiting it economically.
Entente: a friendly understanding or informal alliance between states or factions.
Pandemonium: wild and noisy disorder or confusion; uproar.
Condominium: the joint control of a state's affairs by other states.