Alright, I'm willing to say 1619. 1776 was a significant event, obviously, but many significant events take place over the life of a civilization. Constitutional Union, or contract, between colonies didn't begin until 1787. Therefore, 1776 put us on a path to self governance but did not cement an agreement for such a condition.
Another big argument solved by RainmanJr. Your welcome.
American colonies were establish in North America in 1565 by he Spanish and in the 1600s by the British and French. The United States of America was established in 1787. The North American continent has existed for hundreds of millions of years, and was first inhabited by America Indians.