There are times when I am playing, things are going ok, I save and then come back to it. Instead of having the Altarians still Warm in terms of their relationship to me, they immediately declare war.
What gives? If I want to not have war I have to go back to the next recently saved position. It seems to be a glitch that favors those who play for hours at a time.
I can't give a clear answer about it, but I suppose it happens automatically. If you're an evil/demonic empire, they may not like you so much. I like to trade with them first so that we are at relative peace.