A military alliance will allow one faction to trespasse on another's territory without it being an act of war. Economic alliances would allow feeding. I'm not sure what a cultural alliance would do though. Good questions asked. I think that one faction wouldn't declare war on an ally if that ally is at war with another ally because being alone in war is bad. In this circumstance you could help two opposing factions fight and thus weaken each other and sell the intelligence to yet another faction. Diplomacy could make this game alot more complex and interesting.

You mean like a protectorate? Weaker factions and defeated factions could also become protectorates of a nearby much stronger faction or the faction that defeated them.

Cause from what I understand from the small info of the game, those places belonged to the TEC before, but they decided to rebel when the TEC started getting its ass wupped. Therefore the TEC will try to take them back in a war. Like the U.S.A. vs. the C.S.A.