The military parade to mark the Army's 250th anniversary and its convergence with President Donald Trump's 79th birthday are combining to create a peacetime outlier in U.S. history. Yet it still reflects global traditions that serve a range of political and cultural purposes.

Millions of American soldiers have marched in military parades since the Civil War, which marked the tradition as a fundamental ritual of American unity.

NPR's A Martinez speaks with Peter Feaver, political science professor at Duke University, about the history and symbolism of military parades in the U.S. ahead of Saturday's event in Washington ...