After 1800 BC, the Middle Kingdom state weakened and competing regional states reappeared. The causes of the collapse of the Middle Kingdom state are very much in dispute. Some point to the apparent power of local or regional nobles during the Twelfth Dynastymen such as those whose splendid tombs may be seen at Bani Hasan in Middle Egypt, south of the modem city of Minia. However, the evidence that strong, centripetal forces pulled apart the Middle Kingdom state is very weak. Another explanation of the Middle Kingdom's collapse points to a still mysterious people called the Hyksos. Of Asiatic origin, these foreigners become the successors of the Middle Kingdom kings in the northern region of Egypt, dominating this area for nearly two centuries as [)dynasties XV and XVI. Did they take power by conquest? If so, it would explain the collapse of the Middle Kingdom state. However, there is no surviving evidence of extensive warfare at the end of the Middle Kingdom era, nor is there persuasive evidence that a large number of Asians (whether soldiers or immigrants) moved into the Nile Valley from the east at that time.
An alternative explanation for the rise of the Hyksos is the suggestion that the later Middle Kingdom kings recruited Asian mercenaries to serve in their army. After 1800 BC, perhaps during the reign of a particularly weak or inept ruler, or at a time of economic, environmental or militar crisis, these mercenaries might have become so influential in the army or the bureaucracy that they were able to seize the throne for themselves. But however they came to power, the Hyksos kings ruled only the northern part of the country, although they tried to extend their authority into the south. Their states appear to have been relatively stable and prosperous, but they have left behind no major works of monumental architecture.
After 1650 BC, the native Seventeenth Dynasty established itself in control of the Luxor area. Gradually, it extended its control over most of southern Egypt and, around 1600, began to fight with the Hyksos of the north. By 1550, this dynasty had destroyed the Hyksos states and reunified Egypt under its control. Thus the Seventeenth Dynasty brought into being the last great Ancient Egyptian state, the "New Kingdom." The first dynasty of the New Kingdom state. the Eighteenth, was simply a continuation of the Seventeenth Dynasty: Ahmose, its first king (and with his brother and predecessor Kamose, the heroic leader who defeated the Hyksos), was actually the son of one of the last kings of the Seventeenth Dynasty.