Russia is the correct and only answer only if you’re utterly clueless of history and geopolitics.
Oops, what’s this?
Oops. what’s this?
https://responsiblestatecraft.org/us-russia-nato/
https://en.wikipedia.org/wiki/Minsk_agreements
50 prominent foreign policy experts (former senators, military officers, diplomats, etc.) sent an open letter to Clinton outlining their opposition to NATO expansion back in 1997:
George Kennan, arguably America’s greatest ever foreign policy strategist, the architect of the U.S. cold war strategy warned that NATO expansion was a “tragic mistake” that ought to ultimately provoke a “bad reaction from Russia” back in 1998.
Jack F. Matlock Jr., US Ambassador to the Soviet Union from 1987-1991, warning in 1997 that NATO expansion was “the most profound strategic blunder, [encouraging] a chain of events that could produce the most serious security threat […] since the Soviet Union collapsed”