During Tahmasp' reign, he carried out multiple invasions in the Caucasus which had been incorporated in the Safavid empire since Shah Ismail I and for many centuries afterward, and started with the trend of deporting and moving hundreds of thousands of Circassians, Georgians, and Armenians to Iran's heartlands. Initially only solely put in the royal harems, royal guards, and several other specific posts of the Empire, Tahmasp believed he could eventually reduce the power of the Qizilbash, by creating and fully integrating a new layer in Iranian society with these Caucasian elements and who would question the power and hegemony of the tribal Qizilbash. This included the formation of a military slave system, similar to that of the neighboring Ottoman Empire – the janissaries. Tahmasp's successors, and most importantly Shah Abbas I (r. 1588–1629), would significantly expand this policy when during the reign of Abbas I alone some 200,000 Georgians, 300,000 Armenians and many tens of thousands of Circassians were relocated to Iran's heartlands. By this creation of a so-called "third layer" or "third force" in Iranian society composed of ethnic Caucasians, and the complete systematic disorganisation of the Qizilbash by his personal orders, Abbas I eventually fully succeeded in replacing the power of the Qizilbash, with that of the Caucasian ghulams. These new Caucasian elements (the so-called "ghilman" / غِلْمَان / ""servants""), almost always after conversion to Shi'ism depending on given function would be, unlike the Qizilbash, fully loyal only to the Shah. This system of mass usage of Caucasian subjects continued to exist until the fall of the Qajar Dynasty.