You can talk with complete depth, there are many reasons that U.S came into existence.
There are also reasons such as the loyalty of the locals were shifting as they felt different from the British. Moreover, the parliament in England was less interested with the sentiments of Americans, who were treated as a colony.
Later, you can explain that why America expanded.
It can include Manifest Destiny.
Discuss it a bit, later you can also put slavery as it is also considered to be a reason.
It was the set of beliefs that founded U.S and the abhorrence that was created in the hearts of Americans.
