Senior US government officials knew as far back as 2008 that the possibility of adding Ukraine to NATO was seen as a serious “military threat” by Russia, one that crosses Moscow’s security “redlines” and could force it to intervene.
Yet Western leaders continued insisting that Ukraine would join the US-led military alliance, right up until Russia did indeed intervene in February 2022.
At the annual NATO summit back in 2008, the George W. Bush administration publicly called for adding Russia’s neighbors Ukraine and Georgia to the military alliance. NATO’s secretary-general declared that the two countries would eventually become members.
But privately, US diplomats knew that this move would be seen as an existential threat by Moscow, and could provoke Russian military intervention in Ukraine.
The former US ambassador to Russia, William J. Burns, who is now director of the CIA,warned in a February 2008 embassy cablethat Ukraine constituted a security “redline” for Moscow.
https://geopoliticaleconomy.com/2022/02/27/us-nato-expansion-ukraine-russia-intervene/