Were these promises ever written down in a treaty?
No, largely because Bush felt Baker and Kohl had gone too far, or in Baker’s words he had “got a little forward on his skis”.
The final agreement signed by Russia and the west in September 1990 applied only to Germany. It allowed foreign-stationed Nato troops to cross the old cold war line marked by East Germany at the discretion of the German government. The agreement was contained in a signed addendum. Nato’s commitment to protect, enshrined in article 5, had for the first time moved east into former Russian-held territory.