When tens of thousands of Russian troops started moving toward the Ukrainian border late last year, Russian President Vladimir Putin effectively issued an ultimatum: They won’t go home until he had “concrete agreements prohibiting any further eastward expansion of NATO.”
This week, as the US and Russia exchange formal diplomatic letters, Secretary of State Antony Blinken emphasized that “NATO’s door is open, remains open, and that is our commitment.”
But few have been asking why the North Atlantic Treaty Organization (NATO) would want to move east in the first place. What was once a Cold War security pact has become a 21st-century organization with global military commitments and ever more member countries from Eastern Europe. Members of the alliance didn’t always foresee its expansion and, three decades ago, some of America’s most renowned foreign policy thinkers argued that NATO should be nowhere near Ukraine.
Ukraine is a former Soviet republic. It isn’t joining NATO anytime soon, and President Joe Biden has said as much. Still, NATO’s open-door policy — the alliance’s foundational principle that any qualified European country could join — cuts both ways. To the West, it’s a statement of autonomy; to Russia, it’s a threat. The core of the NATO treaty is Article 5, a commitment that an attack on any country is treated as an attack on the entire alliance — meaning any Russian military engagement with a hypothetical NATO-member Ukraine would theoretically bring Moscow into conflict with the US, the UK, France, and the 27 other NATO members.
https://www.vox.com/22900113/nato-ukraine-russia-crisis-clinton-expansion