@dogfishman - I'm no expert ,happy to agree I'm not totally correct .It's a complicated picture which one can view through different lenses .I don't think it's a simple case of Nato hasn't broken any promises ,I think they've justified their expansion .But they have expanded .
NATO said they would not placing nuclear weapons and that is no doubt true but In 2016, we deployed four multinational battlegroups ─ or "enhanced forward presence" ─ to Estonia, Latvia, Lithuania and Poland. In 2017, the battlegroups became fully operational. More than 4,500 troops from Europe and North America work closely together with home defence forces and that the
total force levels across the Alliance have substantially reduced since the end of the Cold War .
With new technology ,drones ,information gathering I wonder what total force level actually means .
www.nato.int/cps/en/natohq/topics_111767.htm
Nato says that the forces are forces are rotational, defensive and well below any reasonable definition of "substantial combat forces."
Several years after German reunification, in 1997, NATO said that in the “current and foreseeable security environment” there would be no permanent stationing of substantial combat forces on the territory of new NATO members. Up until the Russian military occupation of Crimea in March, there was virtually no stationing of any NATO combat forces on the territory of new members. Since March, NATO has increased the presence of its military forces in the Baltic region and Central Europe
www.brookings.edu/blog/up-front/2014/11/06/did-nato-promise-not-to-enlarge-gorbachev-says-no/
Do you have a link to Russia's agreement that you mentioned ?