CIA Director Burns (then ambassador) wrote in February 2008 that Russia would then “have to decide whether to intervene, a decision Russia does not want to have to face.”

Yet a review of the public record and many dozens of diplomatic cables made publicly available via WikiLeaks shows that US officials were aware, or were directly told over the span of years, that expanding NATO was viewed by Russian officials well beyond Putin as a major threat and provocation, that expanding it to Ukraine was a particularly bright red line for Moscow, that it would inflame and empower hawkish, nationalist parts of the Russian political spectrum, and that it could ultimately lead to war.

https://www.zerohedge.com/geopolitical/dozens-wikileaks-cables-show-us-knew-nato-expansion-was-russias-bright-red-line