The two world wars damaged the case for imperialism, so ever since, wars of aggression have typically been sold to the public as wars of liberation. The aggressor isn’t trying to add territory or exploit resources; it is seeking to free the working class, or an oppressed ethnic minority, or the entire country from a tyrannical, unrepresentative government.
But Putin’s invasion of Ukraine is a blast from the past. He isn’t arguing that the invasion is necessary to protect ethnic Russians from the Ukrainians. He isn’t fighting to restore rights to which Ukrainians have been deprived by the current regime. He wants to extinguish a state that has the support of the vast majority of its citizens and turn those citizens into the subjects of a new Russian Empire because, well, that’s what they were under the later tsars and the Bolsheviks.
In other words, this is a war of imperialism, pure and simple.