Fustat. For an entire year after that, both sides avoided open conflict, and engaged rather in a diplomatic and propaganda battle. Mu'nis offered promises of safe-conduct as well as recognition of the Fatimids as autonomous rulers of Ifriqiya in the style of the Aghlabids, if al-Qa'im and his father submitted to the Abbasid caliph. Al-Qa'im rejected these overtures, reiterating the Fatimid claims to universal dominion as the rightful heirs of Muhammad. He also sent letters to Fustat urging the Egyptians to rise in revolt, and to the two holy cities of Islam, Mecca and Medina, demanding recognition of the Fatimid claims to sovereignty over the Islamic world. Finally, in late spring 921, the Abbasids launched their attack, capturing Alexandria and then moving onto Fayyum. Cut off in the oasis, al-Qa'im was forced to abandon all his heavy equipment, and with his army crossed the desert to Barqa. Third invasion of Egypt For a few years, the Fatimids continued to launch raids from Barqa into Egypt: in 922 and 928, Fatimid troops fought Abbasid troops at Dhat al-Himam, some west of Alexandria. In 923, the Fatimids raided one of the oases of the Western Desert (likely Dakhla Oasis) and laid waste to it, before the outbreak of a disease forced them to retreat. Towards the end of his reign, al-Mahdi began organizing a third invasion of Egypt, but it was not launched until after his death, in 935. Like the previous two attempts, it was unsuccessful. It was not until 969, when the balance of power had shifted much more decisively in favour of the Fatimids, that another invasion was undertaken, leading to the Fatimid conquest of Egypt. West: Maghreb and al-Andalus Subduing Berber resistance The core territories of Fatimid Ifriqiya were the same as in late antique times, when the area had been the Byzantine Exarchate of Africa: Tunisia, northeastern Algeria, and Tripolitania, which had been highly urbanized since antiquity and were used to regular administration and taxation. Outside these areas, the native Berber tribes resisted fiercely any attempts to impose Fatimid rule. From the sedentary farmers of the Nafusa Mountains south of Tripoli, to the inhabitants of the Aurès Mountains in western Tunisia and eastern Algeria—known to Arab authors as the "refuge of all rebels"—to the nomadic Zenata tribesmen of the central Algerian plateau and the settled farmers of Ouarsenis in northwestern Algeria, the mountainous areas generally escaped tight