Clearly refers to War in Donbas.

Eastern Ukraine is full of ethnic Russians (38%) and Russia-aligned eastern Ukrainians, and so when the central Ukrainian government went through the coup in 2014 and practically severed ties with Russia, many were genuinely unhappy with the government, so much so that they wanted to leave the country.

Seizing the opportunity, Russian paramilitary entered Crimea first (with Russians being the majority on the peninsula, people's support was practically guaranteed), and then tried to do the same on Donbas.

Ukrainian government was obviously not happy about this, and already knew what inaction leads to (total Russian annexation) and launched a military campaign to maintain control of Donbas. To many people of Donbas, however, this was seen not as a unification of a country, but as a brutal suppression of people's will, and so locals commonly sided with the local and Russian paramilitary groups in search of independence or ascension into Russia.

As such, many pro-Russian folks cite this as an act of aggression on the side of Ukraine, one that Russia merely responded to in full in 2022. This sentiment is often supported by Donbas locals, who suffered through severe civilian losses during the 2014-2022 phase of the conflict, many fleeing their home to find refuge in Russia.

This sentiment is not, however, so enthusiastically shared by the rest of the Ukrainians, who suddenly had this war come to their doorstep, escalating the conflict to an all-out war with 40 million Ukrainians in the crosshairs. And then Russia took the mask off, adding layer upon layer of bullshit explanations as to why the whole of Ukraine should lose statehood and become occupied.

What started as "we defend these 6 million people, including over 2 million Russians, from an unjustified act of aggression" turned to "we deny 40 million people independence and statehood, and we're ready to destroy everything to have it our way".