The longest unbroken treaty in U.S. history is between the U.S. and which other country?

Relations between the Kingdom of Morocco and the United States date back to 1786-87. Morocco remains one of America's oldest and closest allies in North Africa, a status affirmed by Morocco's zero-tolerance policy towards al-Qaeda and their affiliated groups. Morocco also assisted the U.S. CIA with questioning al-Qaeda members captured in Afghanistan, Iraq, Indonesia, Somalia and elsewhere during the administration of George W. Bush, who designated the country as a Major Non-NATO Ally.

Formal U.S. relations with Morocco began in 1787 when the United States Senate ratified a Treaty of Peace and Friendship between the two nations which had been negotiated in 1786. Renegotiated in 1836, the treaty is still in force, constituting the longest unbroken treaty relationship in U.S. history, and Tangier is home to the oldest U.S. diplomatic property in the world. Now a museum, the Tangier American Legation Museum is also the only building outside of the U.S. that is now a National Historic Landmark. Morocco is also one of the few countries in Africa to extend visa-free travel to American citizens.

The U.S. maintains an embassy in Rabat, Morocco. Morocco maintains an embassy in the United States at 1601 21st Street NW, Washington, DC 20009.