Israel bombed an air base in northwestern Syria last month. Its rationale was that Turkish forces were preparing to deploy there and would threaten Israel’s northern border. Turkey condemned what it called “reckless Israeli attacks.” Washington stepped in to prevent an escalation, but the incident showed how volatile relations between two of Washington’s key partners have become.

Turkey remains one of America’s most important allies. And one of its most difficult. Turkey possesses NATO’s second-largest military, controls access between the Black Sea and the Mediterranean Sea, and occupies the crossroads of Europe, the Middle East, and the Caucasus. It also increasingly acts as an independent regional power whose interests do not always coincide with Washington’s. Turkey is not an American adversary. But as its military reach expands, the United States must be aware of the risks.