progressed slowly until October 1777, when British defeat at Saratoga and their apparent willingness to negotiate peace convinced Vergennes only a permanent alliance could prevent the "disaster" of Anglo-American rapprochement. Assurances of formal French support allowed Congress to reject the Carlisle Peace Commission and insist on nothing short of complete independence. On February 6, 1778, France and the United States signed the Treaty of Amity and Commerce regulating trade between the two countries, followed by a defensive military alliance against Britain, the Treaty of Alliance. In return for French guarantees of American independence, Congress undertook to defend their interests in the West Indies, while both sides agreed not to make a separate peace; conflict over these provisions would lead to the 1798 to 1800 Quasi-War. Charles III of Spain was invited to join on the same terms but refused, largely due to concerns over the impact of the Revolution on Spanish colonies in the Americas. Spain had complained on multiple occasions about encroachment by American settlers into Louisiana, a problem that could only get worse once the United States replaced Britain. Although Spain ultimately made important contributions to American success, in the Treaty of Aranjuez (1779), Charles agreed only to support France's war with Britain outside America, in return for help in recovering Gibraltar, Menorca and Spanish Florida. The terms were confidential since several conflicted with American aims; for example, the French claimed exclusive control of the Newfoundland cod fisheries, a non-negotiable for colonies like Massachusetts. One less well-known impact of this agreement was the abiding American distrust of 'foreign entanglements'; the US would not sign another treaty with France until their NATO agreement of 1949. This was because the US had agreed not to make peace without France, while Aranjuez committed France to keep fighting until Spain recovered Gibraltar, effectively making it a condition of US independence without the knowledge of Congress. To encourage French participation in the struggle for independence, the US representative in Paris, Silas Deane promised promotion and command positions to any French officer who joined the Continental Army. Such as Gilbert du Motier, Marquis de Lafayette, whom Congress via Dean appointed a major General, on July 31, 1777. When the war started, Britain tried to borrow the Dutch-based Scots Brigade for service in America, but pro-Patriot sentiment led the States General to refuse. Although the Republic was no longer a major power, prior to 1774