The main event that led the United State to take a more active role in the world affairs was World War II, since the US emerged from this war an economic superpower. It was also clear that some nation needed to "fill the void" left by the relative fall of the British Empire.
The Declaration of Independence states that the United States of America is a country in its own right, independent of England, and includes a list of grievances against the king of England, while the U.S. Constitution formed our federal government and set the laws of the land.
