The problem is that the AI is far too liberal when it comes to breaking alliances. And since they almost always seem to have negative attitudes towards them you can't get them back. The worst part is when every single large country in the game is aligned with one another, but none of them will align with you. Take my recent Austria/HRE game. There were 6 great powers in the game, France, Burgundy, Poland, Russia, Britain and myself. All five of those countries were all aligned to the other and every one of them had me as a rival. Now bear in mind that my AE was almost always at 0, since I couldn't expand without triggering a war with every power in the game. Another problem is that nations far too often align with each other right after having fought a war. Take my aforementioned game. The giant alliance of doom was finally broken up when France ended up on the wrong side of a war with the others. When it ended, France had no allies. I intended to DW on them to nab some provinces but by the time a month passed (I had to cancel military access) they were aligned again with all the powers they had just fought. How is this realistic. From Allied to war to allied again in a matter of months.