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Valley Forge was where the American Continental Army made camp during the winter of 1777-1778. It was here that the American forces became a true fighting unit. Valley Forge is often called the birthplace of the American Army.

Explanation:

General George Washington and his weary troops arrived at Valley Forge, Pennsylvania six days before Christmas in 1777. ... Washington picked the spot because it was close enough to keep an eye on British troops sheltering in Philadelphia, yet far enough away to prevent a surprise attack on his own Continental Army.