One winter day in December 1775, months after the battles at Concord and Lexington marked the beginning of the Revolutionary War, the nascent American military formally met its commander-in-chief. A group of Virginia rifleman found themselves in the middle of a massive snowball fight with a regiment of quick-talking New Englanders who ridiculed the strangely dressed Virginians in their “white linen frocks, ruffled and fringed.” The colonies were still strangers to each other at this point: The Declaration of Independence was months away, and the ragtag army representing the rebels was far from formally “American.” The meeting of nearly 1,000...