What important group did selim bring under ottoman control?

I assume you are speaking of Selim I. Selim conquered 2 groups that would have been very important. He conquered the Safavids in modern day Iran. This would was key for the access to the trade routes and the taxes that one could gain from the amount of the goods that passed through. They also gained to Egypt and the fertile growing fields when they conquered the Mamluks. Egypt also gave them access to the ports and again through trade.