Complex sentence: Since the establishment of the United States in 1776, the number of states has expanded from the original 13 to the current total of 50, and each new state is admitted on an equal footing with the existing states.
Split into simpler sentences: Since the establishment of the United States in 1776, the number of states has expanded from the original 13 to 50. Each new state has been admitted on an equal footing with the existing states.