"what if the Chinese discovered America before the Europeans did?"
An interesting question that which is kind of dealt with in the book 1421 by Gavin Menzies who examines a historical theory that the Chinese did in fact reach America 70 years before Columbus and did alot of other impressive things (which they then failed to capitalise on as they then entered their isolationist period). A fascinating read which raises some interesting questions. Its also filled with well supported evidence.
I have always wondered what would have happened if Napoleon had won at the battle of Waterloo
What if Rome never fell. (would civilization be much more advanced???)
What if christianity didnt take off (would most western countries be pagan, jewish, athiest or muslim???)
What if Napoleon went on to conquer America (would it all be one big french-speeking nation?)
What if The space race hadnt ended (would we have landed on other planets??)