Pashtunization also called Pathanization is a process of cultural or linguistic change in which someone or something non-Pashtun becomes a cultured to Pashtun influences.
People become Pashtunized when they settle in Pashtun-dominated areas and adopt the Pashtun culture, either by adapting the Pashto language or absorbing Pashtunwali customs.
Pashtunization is a specific form of cultural assimilation and has been taking place in Pashtun-populated regions of Afghanistan and Pakistan for several centuries.
In the eighth and ninth centuries ancestors of many of today's Turkic-background Afghans settled in the Hindu Kush area (partly to obtain better grazing land) and began to assimilate much of the culture and language of the Pashtun tribes already present there. — Craig Baxter, Library of Congress Country Studies.
Turkic tribes who had long domiciled in Afghanistan and gradually adopted the Pashtun culture, some of them left the area during the Mongol invasion of Central Asia towards the Indian subcontinent, where they built empires such as the Khilji, Lodi, and Suri dynasties of Delhi. They are considered by historians as ethnic Afghans (Pashtuns).
Pashtunization may also refer to the settling of Pashtun tribes onto lands where non-Pashtun tribes live or more broadly the erosion of the customs, traditions, and language of non-Pashtun peoples due to the political power and regional influence of the Pashtuns. This occurred in the Peshawar sub-region in the early 16th century, during the period of the Suri dynasty of Delhi. It intensified in the mid-18th century under Pashtun emperor Ahmad Shah Durrani, when he conquered non-Pashtun territories and established the Durrani Empire.
During the reign of Abdur Rahman Khan in the late 19th century, some Pashtuns settled in the north of the country while Tajiks from the north were brought to the south. This was done for a political reason, mainly to prevent a Russian invasion. In the meantime, thousands of Hazaras left Hazarajat to settle in Quetta (now in Pakistan) and Mashad in what is now Iran.