Well, any number of historical reasons: slavery; violence against indigenous people; colonial sources, such as exporting of natural resources; the actions of a state, which might not be recognised as an authority; or simply inherited property from a time of aristocracy.
Equally, people might reject systems of ownership out of hand, and consider the gulf of wealth causes by those systems to be the product of immoral behaviour.
Ah I see what you mean. I suppose I do identify with both the arguments then. Grateful to be born into a society that is as prosperous and free as the one I live and also cognizant that it was at least partially obtained using ventures that were, by today's standards, morally reprehensible.
Kind of a double edged sword though. Any society that currently allows the gratitude probably has a fairly checked past, even those outside the U.S. Not sure where one line begins and another ends.
Equally, people might reject systems of ownership out of hand, and consider the gulf of wealth causes by those systems to be the product of immoral behaviour.