happens late in the game?
that's par for the course in any Diplomacy game that runs long, sea or land spaces both. If we see a sea zone that has too few bordering zones, that is a problem! If we see pinch points, that is also a problem. But lacking these situations, I see no big problem. It's simply nature of the game. One possible option, look at the games webpage ( http://www.freewebs.com/tomahaha/ww4.htm ) and think about the way the game was actually designed. Yes, I had a long game, standard play in mind when laying it out however, I wanted to achieve several things and I did succeed in those.
I saw a few major problems with large games, dropouts could spoil a good time. A large game of this size could run longer than "most" players interest span (leaders would stay interested but all others interest would wane), having only one player win out of 30some players saw a chance at victory incredibly slight, the standard game you have a one in seven chance of winning or about 14% in this game you have 36 players, 1 in 36 is a measly 3% chance of winning, by adding a 3 player coalition option that chance of taking part in the win rises to a still slight 8%, by allowing a coalition win it added a new element to the game, a political "game within the game"and lastly (and least) it also avoided late game stalemates and apathy.
This odd victory condition was appreciated by some, loved by others and absolutely hated by still others. The "purists" wanted a solo win, they didn't care about the other issues and they had no foresight nor any interest in even trying something new. It really does work VERY well and is a lot of fun if you allow it to be. In fact, this also allows any and all players to have a real shot at the win, stay true to your alliance, work the political angle with your other allies and you may very well see a single center power taking part in a win (and yes that has happened one time)