Vortex Wars

Recently I played in a game. I won't name who the players are to protect their identities, but suffice to say that me and Red had our "domains" between Green's domain. I then made an alliance with Red and pincer attacked Green, killing him.

This doesn't sound fair to Green, and in fact I can see no way he could have escaped the moment I made that alliance.

Any issues with this sort of thing?

No rule or anything, but it is very frowned upon.

unless if you look everyone upside down