1) The victims of imperialism include the peasants/serfs/workers of the imperial core.
2) Europe (and the US) did not 'invent' imperialism, it just invented ways to export it across the world. Chinese dynasties did it as well (successfully enough that most of the victims were completely subsumed into 'Chinese' identities) and it's even older than the first dynasty. It's likely as old the very concept of 'conquest'. I consider imperialism the foundation of the very concept of 'empire'. You can't have empire without imperialism at some level.
3) The West did not 'cause' the Warlords; warlordism is baked in to Empire, it's effectively the 'crash' to the narcotic high of imperial power. You take the drug for the high, you're taking the crash. And yeah, the Western Empires have also devolved into warlordism, it's just economic warlords instead of military ones carving up the organs of power for themselves. Yes I am saying that neoliberalist capitalism is economic warlordism, I will die on this hill.
4) While the common folk suffered just the same regardless as they always have, in terms of state against state, the Western powers imperialising China was less 'came out of nowhere and started beating on us' like it was for, say, the peoples of what became Australia, instead it was 'caught another empire sleeping and jumped them'.
5) That does not change the suffering endured, it does mean that the 'flavour' of nationalism produced in response changes heavily; where 'usually' the victims of imperialism react with the 'positive' nationalism of 'resistance' which usually doesn't swing into the negative side until later (see India's current... whole thing), after 'freedom' or some other resolution is obtained, in the case of China (and Russia, if you see the revolution against the Tsars in a similar light) there existed a much lower 'threshold' for reaching that negative point, as there already exists a kind of 'nationalist baggage' to accelerate the swing.