So I bought EU4 a long time ago because it was on sale and now that I am stuck at home and have nothing to do I decided to finally start playing it. I picked Ottomans because the youtube tutorials I watched all said they were a good choice for a first time campaign. Everything went pretty well for the first 25 years; I ate Byzantium, Epirus, Candar, Karaman, and Serbia without any real trouble. I was getting set to finish off Dulkadir who I have some claims on but then I noticed I had a claim on a Hungarian province that was about to expire so I checked their allies, didn't see anything to worry about (I'm the number 3 power in the world at this point so there's not much I need to be scared of) and declared war. About 3 months in, Castile, one of two countries in the world that rank higher than me, shows up with about 40,000 men and kicks my ass. Turns out Castile is defender of the faith, which I'd never heard of but I looked into it and as far as I can tell, that means if a non-Catholic country declares war on a Catholic country, Castile intervenes automatically (correct me if this is wrong). I reload an old save (no ironman b/c first campaign) and decide to let my claims in Hungary lapse and attack Albania instead because my dumb ass thinks they're Orthodox. Nope, they're Catholic, and once again my entire army is limping back to Constantinople as Castile sieges down all my European provinces. I don't want to go back and attack Dulkadir because it turns out they're allied with Mamluks, and I don't really feel like fighting Mamluks at the moment. I check who else I have claims on and I decide to annex some random Greek islands that belong to Genoa, thinking that I can occupy them in a couple weeks and take them in a peace deal before Castile arrives to wreck my shit. I take Genoa's islands, take over their territories in Crimea for good measure, and beat up their navy which is about a third the size of mine and a lot less advanced. I rack up about 25 warscore, which should be enough to annex the islands but the "relative strength of alliance" factor means that as long as Castile is on Genoa's side, they will essentially never surrender; they won't even take a white peace. Basically all my expansion in Europe is on permanent moratorium because every country I could possibly expand into is being baby-sat by Castile (the only non-Catholic countries in the Balkans are Serbia, which I already conquered, and Wallachia, which I'm reluctant to attack because I know Hungary has claims on it and I don't need to give them a reason to attack me). So my question is, is there any way to fight a Catholic country without a DotF intervention? Is there some special CB I can use? If I somehow got a truce with Castile (which is itself a long shot since any war I get into with Castile basically doesn't end until I cease to exist) and then declared war on another Catholic country before the truce expired, would that keep Castile out of the war? Alternately, is there some diplomatic trickery I can pull off so that Castile loses DotF status? The only option that really comes to mind at the moment is converting to Catholicism, and since all my provinces are currently either Sunni or Orthodox I suspect that would be more trouble than it's worth.