For sure one of the most controversial facts in Spanish history is the conquer of a great part of America. I have very mixed feeling about it myself. I cannot justify it. I detest any form of imperialism, colonialism or interventionism, and that conquer was nothing like that. I detest the hypocrisy of using religion as an excuse to justify the quest for gold.
On the other hand, I realise that Cortes and Pizarro could conquer huge empires like Aztec or Inca with very few people only because local tribes who were oppressed by them helped the conquerors. That's the wheel of life, you conquer and then you are conquered. And also I cannot omit saying that Spanish conquerors were not as brutal as other European ones. Look at how many mestizos there are in the lands under Spanish domination and those who were about British ones and get your own conclusions.