Imperialism itself wasn't what introduced blacks into America, they were introduced by Jewish slave traders who bought them from African tribe leaders. Canada and Australia are unquestionably a product of imperialism, yet they have basically no blacks as slavery was already banned when their colonization really kicked off, and Canada and Australia used to be almost 100% white until the recent non-white mass-immigration.

Imperialism doesn't have to lead to large-scale miscegenation either. The former Spanish and Portuguese colonies mostly consist of mestizos today, because the Spanish and Portuguese sent mostly single men to their colonies and let them fuck anything that moved. The Anglo colonies, on the other hand, prove that it's perfectly possible to maintain racial purity under imperialism, by sending both men and women from the UK to the colonies, and by having a "racist" value system that condemns whites who miscegenate as race traitors and punishes non-whites who try to miscegenate with whites. Hence why even the US, despite its large slave-descended black population, used to be over 85% white until the 1965 Hart-Celler immigration act (read: white genocide act).

The idea that non-white mass-immigration into white countries is just a natural consequence of white/European imperialism, rather than something deliberately facilitated by subversive, malicious Jewish elites in order for them to gain more control over the whealthy white countries, is basically just woke anti-white nonsense. Don't let anti-whites guilt you into blaming our people for all our current problems and defacing our own history. I still appreciate it that you still support Columbus Day even though you morally disagree with him though, that's the unapologetic nationalist spirit I want to see more in our circles. For the same reason, I'm against slavery but at the same time I'm strongly against tearing down statues and monuments of Confederates.

Regarding imperialism itself: Even if you morally disagree with imperialism in principle, it's basically a tragedy of the commons. If we as whites are unwilling to reclaim our dominant position on the global stage, which would also mean either directly or indirectly taking back control over most non-white countries we used to occupy, some other race or civilization (such as the Jews or the Chinese) is going to take our place and do it anyways. So if you're opposed to white imperialism/colonialism, what you're essentially implying is "I want whites to be powerless and get dominated by the rest of the world, and I want more power to the Jews and the Chinese!", which is inherently contradictory to being pro-white. I'm not saying you think like this or that you aren't pro-white, I'm just taking the idea of being white and being against white imperialism to its logical conclusion.