Just guessing here, off the cuff riffing, but “a heavily reinforced defensive line was built down the eastern flank of Ukraine” could be thought of as a provocation if Russia considers that region as it’s sovereign territory, or at least disputed, territory. It’s probably one of the reasons Putin held a referendum (whatever you think of its legalities). The people in that region are largely Russian speakers; maybe Russian Orthodox Church members, ethnically Russian vs ethnically Ukrainian. And now Zelensky has reportedly taken pretty serious anti-Russian ethnic line such as banning Russian language and crackdowns on some churches and the like.
It could be argued as an outside observer that it is “disputed territory” though I would perhaps not go that far since it wasn’t really disputed much or not very loudly; except to say that all of Europe’s borders have changed and been in dispute since before the rise of the Roman empire. And of course, Russia did invade Ukraine back during the Obama years without much of a peep from the west. That was some kind of signal - either that we quietly agreed, or that we didn’t think it was worth fighting over. Either way, our government now sure has a different attitude about it today - even arguing that Ukraine should take back the territory taken during Obama’s term.
Stop it, all of you. We did not “provoke” Putin, or force him into war. He saw weakness from Biden and took his opportunity, that’s all.