One of my favorite authors, Arthur C. Clarke, co-wrote a novel recently, well it's a dual novel, Time's Eye (1) and Sunstorm (2).
Synopsis:
Earth is carved up in time with a patchwork of different eras colliding...from prehistory to 2037. 3 UN peacekeepers find allies in 19th c. British troops and eventually the army of Alexander the Great. Meahwhile 3 Cosmonauts join with the Mongol horde led by Genghis Khan. Both sides set out for Babylon, while some unexplained entity watches and waits...sort of like an ultimate pay-per-view battle.

I liked it and recommend it anyways. He really knows the nature of man, yet our potential as well.