The nub of this war is whether there was an understanding (not a written contract) if the USSR agreed to EastGermany on unification of Germany joining NATO that NATO would not move "one inch" eastward after that.
IMO that agreement was understood/accepted by both parties then and hence no need for a formal (written} agreement . Had there been dispute then , IMO there would be a written agreement/disagreement to that extent .
The context of the understandings are documented below by Wikipedia as follows with the bottom line being "if you cant take a country on its word then why should accept its written agreement"? According to Wiipedia policy, if others can refute this by providing authorative documentation then Wikipedia will gladly amend this report.
