Online Manual (http://www.tresebrothers.com/star-traders-4x-empires/game-manual#Alliance) reports effects of this conflict as:
+2 RP per Colony
+2 EP Per Colony
+4 Credits per TP
-10% Colony Maintenance
However, the Templar library reports that there is a 10% reduction to ship maintenance AS WELL as colony maintenance. If this is accurate, it makes the alliance a far more attractive option vis-a-vis the trade alliance.
I believe that the in-game documentation is correct and the online manual is not. If I had permissions, I'd fix it myself. Since I do not, I can only submit this as a request.