No default garrisons, so most colonies are defenseless and you can use a rapid assault force to bypass the enemy ships and steal 5 or so planets and just destroy the colonies instantly if you don't think you can hold them...
and while I believe there is a War-Weariness figure in the background telling the AI to eventually make peace if nothing is happening and the war is going on a long time... there is no game-mechanic active on the player. Colonies only "rebel" because of enemy culture as far as I can tell.
No matter how low your morale, planets will never secede/rebel and no matter how many wars you are in, morale/productivity/etc. is never hampered. Your incredible democracy or tyranny enjoys the political support of your people 100% so long as taxes are kept at a good rate... never mind the fact that you might be losing a war to genocidal aliens, or that your peace loving people have been genocidal wiping out alien civilizations... no one cares lol.
Galactic Civ is a pretty great game, I love it to pieces, but it is missing some basic ideas from typical 4X or other Civ style strategy games and how the game treats population management (virtually none) and diplomacy (including culture takeovers/etc.) is pretty weak.