State Department Background Note on Morocco:

U.S.-MOROCCAN RELATIONS
Morocco was the first country to seek diplomatic relations with the Government of the United States in 1777, and remains one of our oldest and closest allies in the region. Formal U.S. relations with Morocco date from 1787, when the two nations negotiated a Treaty of Peace and Friendship. Renegotiated in 1836, the treaty is still in force, constituting the longest unbroken treaty relationship in U.S. history. As testament to the special nature of the U.S.-Moroccan relationship, Tangier is home to the oldest U.S. diplomatic property in the world, and the only building on foreign soil that is listed in the U.S. National Register of Historic Places, the American Legation in Tangier (now a museum).