For one of my longer stories (well, it may even end up being a novel) I needed a reason for a war between formerly allied races. The situation is following: Few decades ago the Isterians (aliens) were at war with the Garens (other aliens). The Garens were technologically superior and were winning the war, but with quite large casualities. They have decided that the war is too costly, so they tried a different way to beat the Isterians - they have managed to create and spread a plague that made 99% of Isterians sterile. They have retreated and now are waiting for their enemies to die out. The Isterians can't fight back, because they don't know the location of any Garen worlds. Few years later the Isterians meet the humans. They quickly ally with them against the Garen threat by assisting them in a war against rogue human colonies. What I need now is for the humans to enter war with the Isterians before the Garens reappear. What I have come up with: The humans have made projections about how the war with the Garens would go and found out that the depopulated Isterian colonies won't have any chance and will fall immediately, giving the Garens forward bases for the war. So they come up with an offer to make the colonies their military bases and deport the population to the Isterian homeworld. The homeworld actually agrees (for historical reasons - the colonies were quite independend and the homeworld has always wanted to control all of the Isterian population - there were several civil wars between the homeworld and the colonies. They have only formed a military alliance because of the Garens). While the homeworld military complies, the colonies' government and military refuses to. A war begins between the humans and Isterian colonies. The homewrold remains neutral. This scenario is quite interesting in a way, because the colonies' military has a difficult choice to make - either fight and weaken both allied races before a coming war, or surrender and betray all of the colonies' principles. But: Is this plausible?