"50 key dates of world history" sparks discussion

What are the 50 key historic events in world history? Historian Richard Overy, editor of The Times Complete History of the World, thinks he knows.

From the invention of the wheel and plough in 3500 BCE to the collapse of Communist regimes in Europe in the late 1980's, it's a controversial list. The Norman invasion is missing, but the introduction of the oral contraceptive pill is included. Which dates would you add, and which would you remove? Read the complete list online.