The Battle of Monocacy: The Fight that Saved Washington D.C.

From a channel Lumen includes in full: Gettysburg National Military Park's rangers and historians present full lectures, battlefield walks and Winter Lecture Series talks on the battle and the Civil War.

A 52-minute video from GettysburgNPS's catalogue; the title names its topic.

Video by GettysburgNPS, played through YouTube's embedded player.