After looking closer at it,
I'm actually surprised that Protestants don't start the war. May be it's because they chose the leader very badly? England is weak in my game, I've beaten them several times and there is truce between us now.
It's 1614. The leagues were created in 1595.
Catholic league big shots: Amsterdam (me, leader), Ottomans, Spain, Portugal, Austria, Venice, Hungary, Bohemia, Papal State.
Protestant league big shots: England (leader), France, Denmark, Russia, Poland, Norway.
I think Protestant should attack, they are not that weak (apart from England).
I just noticed that one of my colonial nations (I have 7 total) is in top 10 by military size