What is the Russian S-400 Air Defense System, and Why is the U.S. Upset Turkey Bought It? By Siobhán O'Grady – Washington Post
A Russian plane carrying the first components of the S-400 surface-to-air defense system landed in Turkey on Friday, in a move that is opposed by the Pentagon and could damage Turkey’s relationship with the United States and other NATO allies.
Washington has long warned that if Turkey were to acquire the Russian system, the United States may impose harsh economic sanctions and revoke Turkey’s participation in U.S. military programs.
Here are some key questions and answers about how the S-400 ended up in Turkey and what may come next…