Independence Day is a very historic day. But it is an exceptionally historic day for the United States. On July 4, 1776, it marks the day when the Declaration of Independence was signed, and the United States got freedom from the UK, and had its own national sovereignty. They were no longer controlled by the UK, and could control their own actions, and what they wanted to do.
The US getting freedom from the United Kingdom, meant the “US” government could control their own actions, without another country/territory ruling them. However, before the US got freedom from the British, the US was being treated terribly. The UK would make their own constitution and impose it on the