<P> In the 7th--9th century, Islam gave the Arabs a newfound zeal and desire to conquer . They expanded to the territories in the Levant and Egypt . The Arab invasions led to the loss of Egypt, Syria, Palestine and for a short period of time, Crete, Sicily, Cyprus and Asia Minor . Though Asia Minor was recaptured and substantial parts of Syria and Mesopotamia either taken back or subjugated, Egypt remained firmly in Arab hands as did the rest of Palestine . The loss of Egypt was a major blow to the Byzantines since the province of Aegyptus had provided much of the Empire's manufactured goods and natural resources, especially grain, ever since the times of Roman Antiquity . Conversely the Arab acquisition of Egypt gave the Ummayad and later Abbasid Caliphates huge resources, meaning that the Byzantines had to direct large amounts of resources to stave off constant Arab incursions into Asia Minor and Syria . When the Fatimid Caliphate broke away from the Abbasids the Byzantines were able to launch successful offensives into Syria and Palestine, due to this division amongst their enemies . </P> <P> As far back as the invasion of Africa by Belisarius, foreign soldiers were used in war . While foreign military invention was not an all together new occurrence, the reliance on it, and its ability to damage political, social, and economic institutions were dramatically increased in the 11th, 13th, 14th, and 15th centuries . The 11th century saw increasing tensions between Courtly, and Military factions . Until the mid 11th century the empire had long been under the control of the Military Factions with leaders such as Basil II, and John I Tzimiskes, however the crisis of Basil II's succession led to increasing uncertainty in the future of politics . The army demanded Basil's daughters remain in power, leading to a number of marriages, and increasing power for the Courtly faction . This culminated after the failed Battle of Manzikert . As civil wars broke out, and tensions between courtly, and military factions reached a zenith, an increasing demand for soldiers led to the hiring of Turkish Mercenaries to fight internal civil war . These mercenaries aided in the Byzantine loss of Anatolia by drawing more Turkish soldiers in to the interior of the empire, and by giving the Turks an increasing presence in Byzantine politics . These interventions also led to further destabilization of the political system . </P> <P> Reliance on foreign military intervention, and sponsorship for political motives, continued even during the Komnenoi Restoration, Alexius I utilized Turkish mercenaries in the civil wars he participated in with Nikephoros III Botaneiates . In 1204, Alexios IV Angelos relied on Latin soldiers to claim the throne of Byzantium, leading to the sack of Byzantium, and the creation of the successor states . After the resurgence of the Byzantine Empire with the ascension of Michael VIII Palaiologos reliance on foreign sponsorship increased still more . At this time it was common for emperors to seek sponsorship from Venice, Genoa, and the Turks . This led to a series of disastrous trade deals with the Italian states; drying up one of the empire's final sources of revenue . This further led to competition between Venice, and Genoa to get emperors on the throne who supported their respective trade agenda to the detriment of the other, adding another level of instability to the Byzantine political process . </P> <P> In spite of its grievous losses of territory in Egypt and the Levant, the Byzantine empire successfully re-established itself against the threat of Islam under the Macedonian dynasty in the 9th and 10th century . But in the 11th century, a new threat arose as a consequence of the Turkic expansion out of Central Asia . The Seljuks, a division of the Kankalis branch of Oghuz Turks, profiting from both the breakup of the Abbasid Caliphate and the absorption of the Byzantines with internal crisis and the loss of Italy to the Normans, managed to establish themselves in Asia Minor . </P>

Which area failed to establish a centralized territorial state by the end of the 15th century