Well, that's a difficult question because, opinions and ideas change over time especially throughout the 19th century where expansionism and colonialism was the new craze in European nations. All I can say is that from what I know, it started off as Europeans landing, exploring and declaring lands being part of expanding empires, they thought they were educating and bringing civilisation and its wonders to these "primitive" peoples. Soon in most colonies (especially south American and central american) it turned to a rush for resources by any means necessary to fuel warfare between said European states, the means including enslaving, pillaging and conquering by force. Over time slavery became a norm, but by the late 19th and even mid 19th centuries ( France even abolishing slavery in 1842 ) Culture shocks reappeared between European states on the ethical question of slavery. A good example is the Boer wars in south Africa between ethnic Dutch settlers believing they were pushed out of their lands by the British Crown and strongly in favour of slavery fighting the expanding british empire seen as the most liberal of empires abolishing slavery and including all peoples as "citizens of the empire".