To start: I am mestizo, descended from central American Mayans and the Spanish conquerers - this is not a question alluding to white or european supremacy. I have always wondered (I played lots of Age of Empires growing up), however, why it was that European nations like france, russia, britain, portugal and more has both the resources (more advanced military/transportation technology) and the motivation to conquer and colonize the rest of the world. Why couldn’t the Zulu, the Aztec, the Mayans, Australian aborigines etc. defend themselves? Why we’re sub-saharan african nations conquering the continent of europe?
Oh dear. I'll be frank with you: the reason why you haven't received an answer to this question is because the answer would be enormous. You could spend the rest of your life studying how these questions apply to but a single group of people - like the Maya - and never arrive at a definitive conclusion.
I'm a bit occupied at the moment but I want to point you in the direction of a series of posts I made a while back. A redditor asked why people in the United States do not say that native peoples were conquered, another user replied incorrectly, and I offered a brief overview of how Europe responded to the conquest. I think the linked reply will give you a taste of how complex the "motivation" question is.
But the real issue I want to discuss is the "why couldn't indigenous peoples defend themselves". Again, I want to point you to a post I made on that thread which contextualizes the topic you are talking about. After you have read that material, why don't we see what questions you have and we can go from there?