There is a simpler way to view this. Both the US and Russia were playing Realpolitik. Apparently the US did not take the Russians seriously. This was a mistake. In Realpolitik, mistakes generally result in war, sometimes disastrous wars. Similar mistakes occurred in 1905-1914, the 1930s, the 1950s, and so on up to the present mistake.

As long as people follow psychopaths -- which is what Realpolitik is -- the mistake will be repeated. No use going into the details.