NATO

http://www.theatlantic.com/international/archive/2014/03/no-american-weakness-didnt-encourage-putin-to-invade-ukraine/284168/ : Baker promised Soviet leader Mikhail Gorbachev that if the Soviets allowed Germany to reunify, NATO—the U.S.-led Western military alliance that took form after World War II—would not expand “one inch” further east, not even into the former East Germany itself.