Probably money, but that doesn't exclude the obvious racism it created. In Denmark, we had Africans in cages displayed in the Tivoli amusement park in central Copenhagen, so people could look at the spectacle that was the black person (https://nyheder.tv2.dk/samfund/2017-03-31-de-sendte-bud-efte..., in Danish).

While this was not the intent of our colonization and slavery-business, it inevitably caused it, imo. Or, the racism caused the success of colonialism, because it justified it.