Just wanted to provide an update to my post. I located the origins of my Davids. My great-great-grandfather, John David, was born Jean Julien David on January 6, 1840 in Nantes, France. He served in the Union Navy during the Civil War and lived out the rest of his life in Brooklyn, NY. I'd love to hear from anyone related to this person and anyone else with David relatives from the Nantes region in France (I've since found out that Jean Julien's ancestors were mostly from Orvault, a suburb of Nantes).