While there are plenty of historical topics U.S. citizens agree on—generally, events and figures from the Civil War up to the end of the Cold War—the birth of the nation isn't one of them, according to a new report from Johns Hopkins SNF Agora Institute and a nonprofit called Millions of Conversations. The country's founding has become one of the most polarizing eras in history, the new research finds, just as the United States is starting to celebrate its 250th anniversary this year.