Blood tax was the practice by which the Ottoman Empire took boys from their Christian families, who were then converted to Islam with the primary objective of selecting and training the ablest children for leadership positions, either as military leaders or as high administrators to serve the Empire.
These kids gained a lot of power and as a group they maintained that power base. Many of them married into the family of the Sultan.
In this context it is relevant to know the ethnicity because it must have been comforting to their family that they did well. It will have served as a stabilising force in the Empire.
It feels really awkward to specify the ethnicity of people. People are equal, right? So much so that the property Ethnic group is considered controversial in Wikidata because it is so easy to abuse.
- Mr Obama is half black and half white. Does that not qualify him more as an American than as an Afro-American?
- Mr Morsi would not qualify himself as an Arab but as an Egyptian and a Muslim first.