Good write up but I don’t really think the fascist - appeasement thing is a valid comparison.
Just because a country aggressively invades a country does not mean they will necessarily invade another. For example US invasion of Iraq. US obviously is a dangerous country but there hasn’t been any other invasions in the last 2 decades and it doesn’t look like there will be another in the foreseeable future. (I know Afghanistan is an invasion too but not on the same scale. Hundreds of thousands of troops were deployed in Iraq, similar to Ukraine)
Second, we must look at the context behind the invasion. Like you pointed out, this is essentially a war of independence. Ukraine has always been in Russian sphere (if not outright part of Russia) and is considered a geostrategic + ideological priority for Russia. Kiev for example is the birthplace of the Russian people.
So it makes perfect sense that they would try to keep the country in chains and we see the start of the invasion back in 2014 because of the coup that took out the pro-Russian government.
These circumstances are not really going to crop up again. No country but Ukraine (to a lesser degree, Belarus, but that is firmly in Russian sphere) holds as much significance to Russia.
The only realistic thing Russia would go to war for going forward is to keep old Soviet Republics (like Georgia) in line.
Keep in mind if we’re reciting 20th century history as if it’s the Bible on how to act towards aggressive countries - that Germany annexed Austria peacefully. They annexed Sudetenand (sort of) peacefully. When they invaded Poland they did so with relative ease and without losing a significant amount of their fighting power. Iirc it only took them about a month to finish their invasion of Poland. Contrast that to the Ukraine v Russia War where we’ve entered the 2nd year with no signs of stalemate easing up.
Throughout all of their territorial expansions before WW2, the Germany military force did not get significantly weakened.
The Russian invasion of Ukraine, however, has been a disaster for Russia. They are desperately burning through Soviet stockpiles of tanks from the 50s or even earlier. It might take decades for them to return to their previous fighting strength.
I really don’t think it’s likely Russia starts another war any time soon. So trying to compare this with Nazi Germany and “appeasement” I think is a bit reductionist. The circumstances are different.