Random triggers without anything to affect the odds always seem ridiculous to me. Doesn't matter if Relations are at +140 or at -70, doesn't matter if we've got other wars on our hands to deal with, doesn't matter who is in the cabinet, doesn't matter who has how many troops, it's still a 50% chance. Sorry, that's not good for a "plausible" scenario. I want to see at least one or two outside factors affect it (the more the better), so if it makes no sense for it to happen, the odds are abysmally low or non-existent, and if everything adds up to make it seem likely, it will probably happen.
I really disliked how in EU3 and several other games, the odds of things happening were only slightly affected, if at all, by circumstances. You could have +200 Relations with a country, a Royal Marriage, no conflicts or mutual cores, an alliance, military access in both directions, a long history of cooperation in war after war, and a large mutual adversary waiting on the doorsteps of both for the first sign of weakness, and your "ally" might suddenly decide to break all diplomatic ties and attack you, just because the RNG came up with an extreme value. I don't want to see "purely random behavior" passed off as "plausible alternatives" in yet another game.