Fulfill protection treaties. Either put "boots on the ground" or don't promise to in the first place.

Ukraine gave up deterrent weapons (world's 3rd largest nuke stockpile) on promise that the USA would fill the strategic power gap accordingly. Latter didn't, Russia doesn't care about mere "sanctions" in light of empire-building goals, there's only one thing that stops such "acting out".

The US meanwhile continued to expand NATO and attempted to box Russia in. Contrary to the agreements you mention.

Who exactly is building an empire here?

Boots on the ground probably will be the answer in the end. And when people see what it produces they may finally come to their senses.

Separate interests, perfectly and fairly satisfied, rarely favor everyone involved. NATO and Russian sovereignty & protection interests involve conflicting desire to control border areas, as both are suspicious of the intentions of the other. NATO having all but abandoned Ukraine, Russia is emboldened to re-take that buffer area, putting boots on the ground where answered only by rhetoric.

"The world" probably doesn't care about punishing Russia. That's the sort of thing that makes Republicans hard but the average guy on the street has bigger things to worry about.

Certainly, westerners being told they can't go on holiday to Russia or buy Russian made software or other things is not going to suddenly make the people in east Ukraine decide they actually love the unelected government they got landed with.