Chingis Khan
Scourge Of The World
I was at war with my neighbors, the damn dirty Greeks, and I had payed the rest of the world to gang up on them also (rogue state strat). The problem was that I had a fairly largish empire and everyone else had to cross my territory to get to the Greeks. I didn't mind all their troops marching across my land but they were taking to long to be of any use. I signed ROP's with a couple of them and once they were able to use my roads, they were knocking on Athens' front door! The best part was that any annoying Greek units that sneaked behind my front lines to tear up my land and terrorise my workers were cleaned up by my allies crossing my land! We were all in the middle ages so war was taking quite a while and by the time we had all smashed the Greeks and taken our cities, the ROP's were due to retire. Now I retired the ROP's and trapped the armies of the Chinese and the Romans on the far side away from their homelands! I started another war with the Romans, payed the Chinese to join in, and watched with glee as the two trapped armies duked it out as I marched towards Rome. Since their army was trapped away from their homeland, it was plain sailing. Anybody else used ROP's/Alliances to good effect? 
