What causes war-mode?

I have a question, what causes warmode? Okay, naturally you have the situation where a single player goes up and attack a tower. Still, I got a lot of guildies who want to help assist defending/attacking other bases, and they don't want to put us into warmode because of some mistake. Usually it would be enough to:

1) terminate all pets
2) turn off auto attack
3) focus on enemy targets instead of towers

Still there is those who claim that if you just nuke towers, you don't enter war-mode. So, question is, what are the rules for war-mode?