The “13” in America250 history refers to the Thirteen Colonies.
These British colonies along the Atlantic coast declared independence and became the original states of the United States. They were New Hampshire, Massachusetts, Rhode Island, Connecticut, New York, New Jersey, Pennsylvania, Delaware, Maryland, Virginia, North Carolina, South Carolina, and Georgia.
The colonies did not all act identically before independence. Their delegates debated independence, and some colonial governments initially lacked authorization to support the move. Congress ultimately adopted the Declaration of Independence on behalf of all 13.
The number is sometimes confused with the 50 states that make up the modern United States. America250 focuses on the nation’s founding in 1776, when the political union consisted of these 13 former colonies.