I will copy paste this comment from Hexbear that explains how we reached that situation, because I believe it will be useful here for context:

The following three parts are absolutely crucial toward understanding the ongoing war in Ukraine from a materialist and historical standpoint:

One, the Maidan Coup happened in 2013 because the former president Yanukovych wanted to postpone signing the EU association trade agreement, which was an economic warfare against both Ukraine and Russia. First, it required that Ukraine take on IMF loans that required them to cut social spending and education. Second, it would allow European goods to flood Russian market due to the existing tariff-free agreement between Ukraine and Russia, without allowing Russia to do so in reverse. Putin did NOT oppose to Ukraine signing the deal, he offered a tripartite meeting to discuss this tariff issue, but the EU refused. Yanukovych did not want to lose the trade revenue with Russia, so he said he needed more time to talk this out with Russia - but it was already too late, merely postponing was enough to trigger the ultranationalists/fascists to launch a coup.

Second, the Donbass separatists rebelled because immediately after the coup, one of the first things the coup regime did was to initiate a ban on Russian language to lash out against ethnic Russians. Russia was forced into the conflict, because there would have been a massacre if the civil war was to allow the military to crush the resistance in Donbass.

Third, the Minsk agreements showed that Russia was absolutely willing to return Donbass (but not Crimea for obvious reasons) to Ukraine, although Ukraine has to give the Donbass local governments more autonomy to protect their local cultures (so that someone from Kyiv can’t just simply impose a national ban on language or culture without considering the local populations). They waited 8 years for Ukraine to start implementing the protocol, but instead what they saw was NATO openly arming Ukraine for 8 years - this showed that Ukraine wanted to take back Donbass and Crimea by military force, and the only reason for that is quite simply that they wanted to ethnically cleanse the Russian culture without having to adhere to the Minsk agreements. Both Merkel and Hollande, guarantors of Minsk II, have admitted publicly in 2022 that Minsk was simply to buy time for Ukraine to militarize, proving Russia’s intuition correct.

The war in Ukraine was inevitable. Russia still did the last ditch effort in 2021 to call for a security meeting with NATO, but to no avail. Under the new Biden presidency, Zelensky had been emboldened to talk about Ukraine joining NATO and rearming with nuclear weapons, prompting the invasion from Russia in February 2022. The rest is history.