By the end of the 3rd millenium B.C. a large scale migration took place mainly from North Europa to the mild weathered south. One of the strong elements of the Indo-European people, Hittites gravitated to Anatolia through Caucasia while Hatti principalities were ruling the land.
These newcomers did not invade the land suddenly. They settled along side the existing people and set their own settlement units in time. Only after a long time, as a lot of Hittite principalities emerged, they claimed the rule of the land, Anatolia. They never destroyed the existing people and their cities. But instead, they mixed with the Hattis and other people of Anatolia. They even shared their gods, goddesses, art, culture and a large amount of words from Hatti language.
By 1750 B.C. Hittites were the only rulers of Anatolia.