January 20th every 4 years we have the American tradition of transferring (or continuing) power based on public elections every four years. The reason: we are a Constitutional Federal Republic, with state and national governments where we elect representatives to exercise the power of the people and our laws are based on the US Constitution. The 20th Amendment (adopted January 23, 1933) moved the Inauguration date from March 4th to January 20th every 4 years.
Dating back to 1801 and our second president John Adams, we have had a peaceful transition of power at the heart of our government, national election, and inauguration. The reason it fell on our second president is that our first president, George Washington served his two terms and then opted out of presidential limelight. John Adams, former friend and now political rival to 3rd president Thomas Jefferson, was not a fan of his predecessor at this point; however, he set the stage for a peaceful transfer of power in our country. Based on his example, it is now a lasting piece of our democratic history for this political "passing of the torch" to be peaceful for the sake of our country.