On this day in 1818, the United States Congress passed the Flag Act of 1818. This set the number of stripes on the American flag at 13 to represent the original thirteen colonies. The field of blue contained 20 stars for the number of states and continued to grow until the current field of 50 with the addition of Hawaii and Alaska.
Up until 1818 the intent had been to add both a star and a stripe for each state. But as the Union grew, Congress realized that was impractical.