Gates said at the security conference in Munich that "One Cold War was quite enough."
Gates's comments come a day after Russian President Vladimir Putin accused the United States of making the world a more dangerous place.
Putin also said NATO expansion to eastern Europe was a serious factor leading to reduced mutual trust between Moscow and the West.
Gates also warned that every NATO country would feel the consequences of a U.S. failure to stabilize Iraq.
Gates said at an international security conference in Munich that a failure to foster the emergence of a stable Iraqi state that can govern and defend itself would result in further conflict in the Middle East and more terrorism.