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There are other similar systems of the time too. The Eastern Roman Empire used to be split into theatres(as in districts not actual theatres) and each theatre was meant to have an army of soldiers who would be given land in exchange for military service(but this system fell into corruption with the theatre commanders buying up the land from these soldiers and hiring mercenaries instead and things like that) Officers would turn these theatres into there own fiefdom and even rebel often enough as well.
The Janissary system itself is sort of similar again to what the Eastern Romans had. They had these theatre armies of course but they also had permanent standing armies of professionals in Constantinople(not just the Varangian but actual Greek units), kind of like the Kapikulu corps.