"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 'U.S./NATO Cooperation with Turkey'), harmonizing priorities can be difficult. These priorities sometimes diverge irrespective of who leads the two countries, based on U.S.-Turkey contrasts in geography, threat perceptions, and regional roles."
CRS Report for Congress, R44000