The US was informed that Russia would be violently hostile to any US or NATO encroachment on Ukraine and other states bordering Russia.
The US should have been actually aware of such sensitivity given that the USA nearly started a nuclear war in the 60s when Russia was installing missiles in Cuba.
The USA provoked the Ukraine war and refused to allow Ukraine to surrender because this would solidify the fact that the USA lost this war.
The USA lied and is still lying to the global and US public.
The 100s of thousands of dead Ukrainians are a human sacrifice to Uncle Sam's vanity.
"Burns, now CIA Director, was US Ambassador to Russia in 2008, and author of a memo entitled “Nyet means Nyet.” In that memo, Burns explained to Secretary of State Condoleezza Rice that the entire Russian political class, not just Putin, was dead-set against NATO enlargement. We know about the memo only because it was leaked. Otherwise, we’d be in the dark about it."
https://www.jeffsachs.org/newspaper-articles/nato-chief-admits-expansion-behind-... Quote:NATO Chief Admits NATO Expansion Was Key to Russian Invasion of Ukraine
The continuing U.S. obsession with NATO enlargement is profoundly irresponsible and hypocritical. And now Ukrainians are paying a terrible price. ...
... In testimony to the European Union Parliament, Stoltenberg made clear that it was America’s relentless push to enlarge NATO to Ukraine that was the real cause of the war and why it continues today. Here are Stoltenberg’s revealing words:
“The background was that President Putin declared in the autumn of 2021, and actually sent a draft treaty that they wanted NATO to sign, to promise no more NATO enlargement. That was what he sent us. And was a pre-condition to not invade Ukraine. Of course, we didn't sign that.
The opposite happened. He wanted us to sign that promise, never to enlarge NATO. He wanted us to remove our military infrastructure in all Allies that have joined NATO since 1997, meaning half of NATO, all the Central and Eastern Europe, we should remove NATO from that part of our Alliance, introducing some kind of B, or second-class membership. We rejected that.
So, he went to war to prevent NATO, more NATO, close to his borders. He has got the exact opposite.”
To repeat, he [Putin] went to war to prevent NATO, more NATO, close to his borders.