With no one to push back on us, we did what we wanted.

The old Soviet Block countries wanted to become part of NATO, which made sense for them. We gladly let them in during 2 expansions and the Russians couldn't do anything about it. But they kept building and when we announced the 3rd expansion (claiming that Ukraine and Georgia would be part of NATO) in 2008, they had had enough. They can read a map and that would put NATO countries along pretty much their entire Western border. And they were now strong enough and decided to push back. Crimea was step 1, then supporting rebels in Ukraine and now this. The more we got, the more we wanted (greed).

Now, to your point about miscalculations. Why do we want to continue to expand NATO? What do we get other than another 2nd rate military we have to prop up? Oh yeah, a client state for arms sales...... (greedy).