A rising number and volume of warnings against making Ukraine a NATO asset also came from Putin and other officials. Washington and its key European allies ignored those warnings, but it became clear in 2014 that the Kremlin was not bluffing. When President Barack Obama and key European leaders helped overthrow Ukraine’s generally pro-Russia president and install a regime subservient to NATO, Moscow struck back emphatically, seizing Ukraine’s strategic, but majority Russian populated, Crimean Peninsula.
Relations between the West and Russia continued to deteriorate thereafter.
Source: Will Armageddon Be Joe Biden’s Final Legacy Regarding Russia?
I've heard different theories on the motivation for Russia's invasion of Ukraine. One has to do with Putin protecting Russians from Ukrainian Nazis. This one seems unlikely, especially given how the war has progressed.
Another theory seems far more likely but makes you wonder what the Biden administration (and others before) are thinking. It has to do with Russia not wanting Ukraine to join NATO and NATO seemingly moving forward with plans to eventually admit Ukraine. This combined with the West's participation in overthrowing a pro Russian Ukrainian government provide Russia's primary motives for invading.
Now I don't think this justifies Russia invading Ukraine and all of the associated death and destruction. Having said that, I don't really understand the motive of the U.S. or NATO of wanting Ukraine in NATO either. It just seems like an unnecessary provocation with no real advantages. The upside is that if Trump really does want to end the war then it shouldn't be too hard to do. I don't think it will be a quick as he says because the devil is in the details but if Trump is prepared to guarantee no NATO admittance to Ukraine then the details could be worked out.
It isn't capitulating to the aggressor to guarantee that we won't do something that we shouldn't be doing in the first place. But like I said, the devil is in the details. The article linked above goes into some more detail on the subject.