The US flag represents the history of the full development of the US. First lets start off by going through what the stripes mean. If you count, you are going to count 13 stripes. Those 13 stripes represent the thirteen original colonies. Those thirteen colonies helped create the US by fighting through all sorts of taxes and wars from Great Britain, like the Revolutionary War and the Stamp Act, and so forth.
There are also fifty stars on the left side of the flag, put into a square. Those fifty stars represents the fifty states of the US. At first there were only thirteen states. But then France's leader, Napoleon Bonaparte gave Thomas Jefferson parts of the northwest land, known as the Louisiana Purchase. What France noticed is that the US had constantly asked for the New Orleans port so that they can trade. The next phase of land was from Mexico. This part of land consisted the land of Los Angeles and all the other southwest parts of the US. While pleading for land, US and Mexico had to go off into the Mexican-American War. When the US conquered they got that land and outstretched the land.