Can you please explain this question? "How did the idea of the Native Americans as devil worshippers justify, to Europeans, the seizure of the infidels' wealth?"
The same logic utilized by Western Europeans to stage the waves of the Crusades was used to take Native American land. At that time (Middle Ages) there existed a socio-economic policy called primogeniture which required a father's assets and wealth to pass to the oldest son, leaving the younger brothers with nothing. This left the younger brothers with two choices: become a priest or enter military service for some powerful Lord. Many entered the military service but this still did not provide sufficient income. These knights (and private armies) took note of the Middle East, which had generated substantial trade with some European nations, especially Italy. It was common knowledge there was significant wealth in the Middle East, but to descend on the Middle East and take their wealth, the armies needed to justify their actions so as to simply mask the real reason (wealth). They used the fact the Middle Easterners were Muslim and NOT Christian and therefore did not deserve their wealth so they went to the Middle East and took the wealth in the name of God. The same approach was used by the Europeans when relocating to America and especially after the Civil War, at which time settlers heading West and the government that encouraged them decided the Native Americans who occupied the land were not using the land as God had decreed (agriculture) and therefore did not own the land and did not deserve to do so. Further, the Native Americans were not Christian and were polytheistic, which provided more justification because if they were not worshipping the one true Christian God, the gods they were worshipping had to be evil, thus they were devil worshippers.