And the Castille/Portugal/England alliance still doesn't stop French expansion the majority of the time.
They can't because the AI is really, really still quite stupid. Portugal will march a 15 stack into France to get wiped, England will land stacks of 15 in France to get wiped, even if they group up a 30 stack isn't going to survive the 55 French stack with their god generals.
Then Castile will march a 17-25 stack into France (the rest of their men will stay standing in Galcia forever), they may or may not arrive in time to help Portugal, but the numbers still aren't in their favour. If Castile has Aragon in a PU, maybe in Art of War they will link up, but normally no, Aragon puts 17 into France, they will join fights in progress but can't do crap if they are killed before Portugal and Castile arrive. Naples will land clumps of 5 men who will be wiped constantly.
Here's how it should work. They all link up in Castile, march together into France, siege territories in clumps of 4-5 so they can back each other up with their 100 units v. France 50, once that fight does happen, leave a few troops in each seige, maybe 5 to guard against France building troops too quickly, and the rest of your men chase the French stack, wipe. Then 2-3 men in every province of France, keeping two units of 10 roving around wiping out any stacks until you get situated, and more men on the Eastern border to guard against a 10 stack coming from Hungary.
Oops, the AI is way too stupid to do that, where as I as Byz managed to wipe the French stack that had been routed by Austria and siege 70% of France while the entire alliance and Austria's 50 men sat in their territory only attack French stacks that formed.
The AI is really, really bad at war, and France can make several doom stacks unless you carpet siege them super quickly. I do that because I want to inherit a strong France, as Castile I let France make troops, and slowly siege the land, a 24 year war that bankrupts France drops them to 0 manpower and destroys them for the rest of the game, but the AI can't do that either.