S-400 issue from a historical perspective

Turkish President Recep Tayyip Erdoğan has declared that the Russian S-400 air defense system will be delivered by July this year, and the cooperation with Russia, including technology transfer, will continue as planned. The U.S. administration is trying to stop or slow down this process with promises, as usual. There is no concrete, genuine step taken by Washington to contribute to Turkey's defense, other than threats of not delivering the F-35 fighter jets whose production's financial burden Turkey is sharing.