"If Christians have a claim over Hagia Sophia, then the entire territory of the United States should be restored to the Indians, as the conquest of the United States happened hundreds of years later."
As if the creation of a modern nation with railroads, highways, skyscrapers, modern technology and the highest standard of living from a wilderness once roamed by people stuck in the iron-age with no written language or even the wheel can compare to the wholesale theft of one of the greatest cities of the classical age can be equated.
Or simply put: We created a nation from nothing. The savages in Europe occupied a nation they could never create if they had 10,000 years.
Without them your skyscrapers would be many fewer in number and far more expensive.
(nitpick) Technically the Native Americans were not in the Iron Age, they had little metal working of any kind. Stone age is more appropriate..