So... are alliance cascades just a problem you have to deal with? I decided to play England, but every casus belli looks as if it would unite half of Europe against me, while my measly few allies barely give a damn. I guess it's safest to ignore them for the while, but what kinds of opportunities should I be looking for when I do want to start reclaiming land?
If you're England you really don't have to worry about this much at all. Just make sure you have the biggest navy in the world by a long shot. Just wreck their navies and if you don't want to face their armies just keep them from landing forces untill they're forced to default into a white peace. Easy!
England is pretty much in the best spot in all of Europe and it's trival to keep invaders off your soil if your wreck their transports and/or navies.
As England I usually just pick off all the island nations and let mainland Europe do it's own thing while I go colonisin'. Come back in a hundred years or so with enough Red Coats to block out the horrizon and reclaim Europe for the glory.
It's good to weaken Castile and Portugal at the start so they won't be competing with your for colonies. Consider an alliance with Granada so you can enter a war when Castile tries to finish the Inquisition.
From there on steal Iceland from Norway and wait for a core, colonise Greenland and wait for a core, then you'll have the whole North of America which nobody will be able to touch for centuries. After you have the Americas the world is your's. remember to oppress those dirty colonials, a free America is an unproductive America.