e.g. I was reading this article
http://www.filmsforaction.org/kolkata/news/fdi_in_retail_who_will_it_hurt_the_most/
As often happened in those times, the Portuguese attacked, looted and set fire to the town of Calicut. The Mappila community lost the spice trade — and a whole lot more — that they had carefully built over centuries to the invaders.
Why?
Couldn't the invaders have also made use of it? Even Genghis Khan or Mahmud Ghazni, other Muslim invaders into India e.g. Were they the consequence of one-sided aggression? Why did they decide to attack a totally peaceful colony?
In another sense, isn't it such a risky exercise? Is it just materialistic greed? If that is the case, how can European invaders be blamed for wipeout of Indigenous tribes in America and Australia? Isn't this a natural way of life?
In the same way, are we affording to much respect to smaller tribal settlements when we need to expand to satisfy the 'greed' of a technologically advanced populace?
It's a very vast question, but I believe the motivations are essentially connected.
I don't have a comprehensive answer, but I can recommend looking at David Graeber's excellent book, Debt. One discussion that stuck with me was how Cortez's barbarism might be explained by the deep debt and corresponding social insecurity of Cortez and his cohort.
The psychology of debt is one of hierarchy and seems to create an urgent need to escape the debt, often at the expense of any who might seem weaker.