Proposal against dirty and vile coalition tactics

Hello, I am playing for the first time in "World in flames - 100 players game". Two players formed a coalition and used backstabbing tactics. They accept you into the coalition, then they tell you to attack a third country. While you do your the coalition duties, they send 20+ armies into each of your main and developed provinces. Then they kick you out of the coalition and at the same time declare war. So they got my whole country instantly and without resistance. In my game this was used twice / against   two countries  / I do not mind a player being kicked out of the coalition, but I think it is right after the exclusion - to have a period / day or two / in which your coalition partners can not to attack you.