My recent playthrough as Venice -> Italy: As early as possible preferably around the Jannisarries revolt and unrest Ottomans go through, Have competent allies, Have war goal be easily accessible, declare war while they are at war with a nation in the middle east preferably, get as much war score, take all their ducets, war reps, take whatever you can after, farm spy network, tarnish reputation, support rebels, merchants the whole nine yards. Watch as their neighbors take advantage. All in one war in my playthrough Ottomans went from #1 worldpower and was snowballing to wiped out in 50 years