Diplomacy?

I'm very confused by the diplomacy situation. I'm currently playing an 8 team game against the computer, and twice now I've had four+ enemies allied (I guess, they pass up each other's planets to get to mine), and the only diplomacy that works is the missions, which become kind of useless when the person they want you to hit is across the galaxy. Are gifts supposed to raise the loyalty meter when there isn't a mission for the gift? Am I missing something in the diplomacy?