"Turkey, a NATO ally since 1952, is significant for U.S. interests. It is a constitutional republic with a large, diversified economy and a Muslim-majority population that straddles Europe and the Middle East. The history of the U.S.-Turkey relationship is complicated. Although the United States and Turkey support each other's interests in some vital ways (see 'Overview of U.S./NATO Cooperation with Turkey'), harmonizing priorities can be difficult. These priorities sometimes diverge irrespective of who leads each of the two countries, based on contrasting geography, threat perceptions, and regional roles."
CRS Report for Congress, R44000