As America enters the 250th year since the signing of the Declaration of Independence, director Ken Burns tells John Dickerson that the American Revolution was a "civil war" that became a "big world war by the end" and more.

Burns and "The American Revolution" co-director David Schmidt walk in Colonial Williamsburg. Burns says he does not take his self-appointed civic duty and his career immersed in wars lightly.

Filmmaker Ken Burns explains the importance of the American Revolution, telling "CBS Evening News" co-anchor and CBS News chief political analyst John Dickerson that he thinks it's "the most important event since the birth of Christ in all of world history.