Circa 1870, the North fought the South in the Civil War. Half a century later, around 1920, worker unrest, racial tensions and anti-Communist sentiment caused another nationwide upsurge of violence. Then, 50 years later, the Vietnam War and Civil Rights Movement triggered a third peak in violent political, social and racial conflict. Fifty years after that will be 2020. If history continues to repeat itself, we can expect a violent upheaval in the United States in a few years.