The Mamluks came mainly from their being taken as prisoners of war or purchased from slave markets. They were brought mostly from the territories beyond the river, i.e. the River of Jaihun (Amu Daria), North of Turkmenistan and Afghanistan, separating them from Uzbekistan and Tajikistan. Those who lived in those territories were mostly Turks, and their territories were a theater of relentless fighting and instability, and this is why there were so many prisoners of war from those territories, which had lots of slave markets. Some of the cities most recognized for slaves were Samarkand, Farghaanah, and Khwarezm.

For this reason, the Mamluks were mostly of Turkish origin, along with some of Armenian and Mongolian origins. There were also Mamluks of European origins known as Saqaalibah, brought mainly from Eastern Europe.

This remained in progress throughout many decades and even centuries. But the main change made by As-Saalih Ayyoob, and the Mamluk sultans after him, was that he brought only the very young Mamluks who were still in their early childhood, mostly from non-Muslim countries. But sometimes, some Muslim children who did not speak Arabic happened to be taken captives, and since neither they nor their origins nor their religion were known, they were treated as slaves.

https://en.islamstory.com/en/artical/20773/origins-mamluks