Ever hear of the Songhai?

They were an empire that expanded, killed indigenous African tribes, and later sold them into slavery to the Moors/Portuguese.

Human history is full of instances where a central power captures a frontier from a lesser, weaker, or more primitive culture.

There isnt anything to apologize for, it is only in the current year where postmodernism has peaked does society feel that their forefathers did something wrong.

Let me assure you, if they hadn't someone would have, that is the paradox of this discussion.

And lets assume history played out by your argument: North America (the parts not dominated by the Aztec or Maya) would be a wasted empty land, and Africa would be filled with mud huts.

Progress sucks, the weak get consumed, the concept of equality doesn't exist in nature, if your culture used flint arrowheads and wasn't smart enough to bend the knee to a more advanced society with guns, you are going to get wrecked. 

Welcome to the jungle.