The past week has witnessed reports of increased Turkish military activity in Iraq and Syria as well as its intruding itself deeper into the war in Yemen. In all three cases Ankara has pitted itself against forces that are or can be seen to be pro-Iranian: Shiite parties in northern Iraq, the government of Syria and the Houthi-led government in Yemen.
Direct tensions between Turkey and Iran have been increasing since last year over the above three nations as well as the Turkish-directed attack on Nagorno-Karabakh by Azerbaijan (Turkey and Azerbaijan identify themselves as "one nation, two states') and its aftermath.
Each time the North Atlantic Treaty Organization has rushed to Turkey's defense over the past eighteen years – holding Article Four consultations four times (one time to "protect" it against Iraq, three times against Syria), maintaining three Patriot anti-ballistic missile batteries since 2013 – it has referred to the nation as NATO's southeastern border. In addition to Turkey having the largest population and the largest military of any NATO member state except for the U.S., it is also the only member of the military bloc to border countries in the Middle East and the Caucasus: Iraq, Iran, Syria, Armenia, Azerbaijan and Georgia. Turkey has invaded the first and third and participated in a near-invasion against the fourth. (Last September a Turkish F-16 shot down an Armenian SU-25, killing its pilot.)
The U.S. maintains B61 nuclear bombs in Turkey under a NATO nuclear sharing/burden sharing arrangement which mandates that the host country provide aircraft to deliver the bombs. NATO also has its Joint Command Southeast and Allied Air Component Command headquarters in Turkey. It moved its Allied Land Command to Turkey in 2012. In the same year it installed a Forward-Based X-Band Transportable anti-missile radar facility with a range of 2,900 miles. This year it handed over the command of its Very High Readiness Joint Task Force to Turkey.