Oh, and Torie, sure competition played a great part, I'm sure (one of the reasons the EU is such as poor idea; it removes Europe's key historical advantage). But I don't think it is solely responsible. The whole germ thing I don't really buy either. Europeans died from stuff they got on other continents too. I think it's more about being the stronger party that determines the outcome of disease-mixing. Sort of being the spreader as opposed to the spreadee, as well as having the advantage of better medical equipment.
And I would give the Greek a little credit too. They did come up with the idea of the city state, breeding the competition that you talk about. 
Germs were a very crucial factor. Why do you think Europeans were only able to settle the Americas and Australia? The thing is that since the population in the Americas were very low compared to the rest of the world, they didn't live in close contact with each others(cities) and thus weren't able to cultivate germs like Europeans, Middle easterners, Indians and Chinese did. Epidemics have always affected society but they become less and less deadly as immunity builds in the population. When the Europeans reached America they inadvertently released all of these deadly diseases at once, diseases that were maybe a mere nuisance to the Europeans themselves. On the other hand they gave us syphilis so damn them.
( Interestingly this disease occurred in the parts of the Americas with the greatest concentration of population, Central Mexico)
Also the reason Europeans took to the sea was due to events to their east. The muslims fought multiple wars and finally took over the trade routes leading into Asia. Thus Europeans couldn't access their priceless peppers of Kerala and the silk of China. Thus they had to think outside the box and which meant sailing into the open oceans. Also Europe is much more susceptible to invasion than either India or China. India is protected on 3 sides with the highest mountains in the world and one side by the ocean. It is a similar case with China. I am not saying there were no population pressures, or they would have been like Native Americas, but not to the extent of 15th century Europe. Facing this population pressure and invasions etc., the Europeans had to innovate or perish.
