France provided covert financial aid to the American colonies before 1778.
France secretly supported the American rebellion because it wanted to weaken Britain after losing the Seven Years' War. Beginning in 1776, French officials worked through the merchant house Hortalez & Cie, associated with playwright and diplomat Pierre-Augustin Caron de Beaumarchais, to send weapons, ammunition, clothing, and other supplies across the Atlantic. French funds also helped sustain the American war effort.
This assistance was deliberately concealed because France was not yet formally at war with Britain. French aid included large quantities of gunpowder and firearms, materials the Continental Army urgently needed. France also helped indirectly by allowing American ships and privateers to use French ports and by facilitating trade.
The American victory at Saratoga in October 1777 changed French calculations. In February 1778, France openly allied with the United States through treaties of commerce and alliance. French troops, loans, supplies, and naval power then became central to the American victory, especially during the Yorktown campaign in 1781. Spain also aided the American side after entering the war against Britain in 1779, but France was the principal European power providing covert support before the formal alliance.