I think there’s a small misunderstanding here. Cowbee is using Lenin’s definition of imperialism, which is different from the commonly understood definition of imperialism. When you say imperialism you likely mean something like “a big country attacking a smaller country”, but that’s not what Lenin (and so also Cowbee) means by it.

Here is a link to Lenin’s Imperialism: The Highest Stage of Capitalism if you’d like to read it. Lenin doesn’t ever give a straightforward sentence or two definition of imperialism (at least, I don’t think he does, I could be wrong), but really, for a first approximation understanding of his definition, I would look to the subtitle, that is “The Highest Stage of Capitalism”. For Lenin, imperialism is the name given to the actions of a growing international bourgeoisie during a particular time in history, a time when capitalism is reaching its full power, and thus also, of course, experiencing the full weight of its contradictions.

It’s a good little pamphlet by Lenin, gotta say! I’d recommend reading it at some point if you get the chance!