I like espionage
Just a bit later down the line, definitely not my 1st...2nd...3rd and sometimes its the 4th but usually 5th idea I take (if i do).
I broke the HRE apart with espionage. I played that game like a CK2 game pretty much lol. Dunno if it was part of MEIOU or the game is just like that as maybe its realistic...but I had everyone hate Australia (the leader of HRE) and they all attacked him. Didn't think HRE would turn on the leader, but they did lol. On top of that, Austria (which was HUGE by the time I got espionage) had so many rebellions (
) that it pretty much crumbled.
One by one I took down HRE
In its place, Lithuania took the eastern part, and for some reason islam owned that game and took over spain and france. But couldn't beat england. Islam (mamluks still survived, and so did Fez) was also very advanced in tech. It outclassed me lol. But maybe I just sucked at it as it was my first game I did with EU4. In any case, they really owned.
And then my save corrupted
(edit: Early on, espionage is definitely rather useless (most of the time). I tried it as Byzantines to take down ottomans. And well, that actually worked VERY well...all of that area had massive rebellions and the entire area fell apart and I took over easily. Wasn't meant to do that good on a test game lol, but ah well.
Next game I tried Cilicia (the armenia guys), and tried espionage against mamluks. But it didn't do anything at all. No rebellions, nothing.
Could depend on the nation, maybe mamluks get high lower revolt risk or something. Or its random. But it sure worked as Byzantines that one game, ottomans (and everyone else in that region (that was islam) got crushed by revolts.)