The Warlords is about the Taiping Rebellion, Forbidden Kingdom is an adaptation of Journey to the West. I suppose you could say that's overkill, but China has a rich and varied history. There's about 1,500 years between Red Cliff and the Warlords. They're both about different things anyway. Red Cliff is a historical drama. The Warlords is more John Woo than John Woo - more like A Better Tomorrow, brotherhood of men, faithful until death, type stuff.
Anyway, Red Cliff is the definitive version of part of the Three Kingdoms story (208 AD to about 210 AD, at least). Or it will be, once Part II is released.