US failure to prevent the Russian invasion of Ukraine is the result of stupidity. Starting with the Biden administration approval of the Nordstream II operations. This was a giveaway to the foolish German government. Even the Obama administration was not so stupid.
There is no upside to this war. Its a loss prevention exercise for all involved.
Korea was only preventable through a completely opposite US defense-strategic stance from 1946-50. If the US had not run down its military forces and support to its allies to the extent it did. That, btw, is also most of the reason the Reds took China, a much greater consequence of postwar US policy.
Since when it is the responsibility of the United States to stop tyrannical dictators from launching wars and engaging in terrorism?
By your logic you failed because you didn't stop some liquor store in Texas from getting robbed.