Many analysts and politicians have suggested that the Alliance reneged on a promise not to enlarge, and thereby provoked Russia. But there never was such promise.
In 1990, the United States and Germany reassured Mikhail Gorbachev that NATO forces would not be stationed in the Eastern Lander after unification. According to then-Secretary of State James Baker’s famous words, NATO military forces would move "not an inch" eastwards. This commitment was enshrined in the "Four plus two" treaty and was always respected. At that time, the Warsaw Pact still existed, and none of its members had declared their interest in joining.