Thats called diplomacy.
Indeed we choose to side with W2V long before they become top tribe in w71. On one side we had players that did not even respect their diplomacy(NAP) toward us, tribes that were trying to recruit Royale members from time to time or were sending mass propaganda mails looking for traitors(and they had some success in the beginning), they threatened to wage war with us from time to time etc. I am not saying that all tribes from khan/stop used dirty tricks on us, but it involved some key accounts in each tribe.
On other hand we had tribe that always had high respect toward us even if we did not have much contacts or coordinations at the beginning. Communications and coordinations between Royale and W2V improved with time without any kind of issues such as those we had quite a lot with VENUS/STOP and KHAN so merge between us was just one final logical step in that direction. It was not even a hard choice.
Anyway first time Vemork and some other of his mates broke NAP toward us by nobling some of our border villages, he started war on us, just has not declared one. It was cold war until condition has been met for open one as indeed we unfortunately had quite a number of inactive/traitors that we needed to take care off in order to be fully ready for it.
I actually am not sure how someone can expect that we side with him after all the things he or his leadersdid toward us. Later excuses like "cooplayer did it without my knowledge" or "we can forget about past for greater good" are actually real BS.
As to other tribes, except to our allies, we were defacto in war all the time all our diplomacy talk with them was with purpose. In war everything is allowed. Thats called strategy and its quite a diferent from dirty tricks and disrespect used against us.
All warfare is based on deception. Hence, when we are able to attack, we must seem unable; when using our forces, we must appear inactive; when we are near, we must make the enemy believe we are far away; when far away, we must make him believe we are near. If your enemy is secure at all points, be prepared for him. If he is in superior strength, evade him. If your opponent is temperamental, seek to irritate him. Pretend to be weak, that he may grow arrogant.
SUN TZU