Why are these dates in hidtory important?

Well you answered your own question with what took place in those years. Each event had an impact in the world not just the nations where they took place. You could also add 1066 to that list of dates but I ain't going to tell you what happened that would take all the fun out of finding out for yourself. lol Sorry, you can tell I have a degree in history and tend to enjoy it just a wee bit much. =)