Have you taken Africa yet? You need Jerusalem in order to win, so unless you want to do a crusading hit-and-run in the final few turns, you should pick up Africa and Egypt before taking Jerusalem. If your navy is large, gobble up the islands as well. Northern Italy, France and the coastal provinces of the Middle East have numerous provinces clustered close together, so grab those. Beat up the Egyptians until they accept vassalage if you don't want to manage all those cities yourself. 65 turns before the campaign ends you'll get world-is-round event. Shuttle 2 stacks of your best troops across to America and capture the six cities there. You should then have more then enough to win.