Under Putin , Russia 's relationships with NATO and the U.S. have passed through several stages . When he first became president , relations were cautious , but after the 9/11 attacks Putin quickly supported the U.S. in the War on Terror and the opportunity for partnership appeared . However , the U.S. responded by further expansion of NATO to Russia 's borders and by unilateral withdrawal from the 1972 Anti-Ballistic Missile Treaty
9/11 attacks
September 11 attacks
Vladimir Putin