Why is the year 1492 considered a turning point in history?

1492 was the year of Discovery of America by Columbus!

This meant that the history of the world, which so far was separate (the one we know, from the Old World, but there was also the history of cultures and civilisations of the New World) was joined: the civilisations clashed and the globalisation begun. It was also the beginning of the end of many American Cultures and languages...but also a beginning for many nations, such as the US and for example, Mexico

Idont know which one is right   but i know that c is wrong and a might be wrong