<P> The Empire soon fell into a period of difficulties, caused to a large extent by the undermining of the theme system and the neglect of the military . Nikephoros II, John Tzimiskes, and Basil II changed the military divisions (τάγματα, tagmata) from a rapid response, primarily defensive, citizen army into a professional, campaigning army, increasingly manned by mercenaries . Mercenaries were expensive, however, and as the threat of invasion receded in the 10th century, so did the need for maintaining large garrisons and expensive fortifications . Basil II left a burgeoning treasury upon his death, but he neglected to plan for his succession . None of his immediate successors had any particular military or political talent and the administration of the Empire increasingly fell into the hands of the civil service . Efforts to revive the Byzantine economy only resulted in inflation and a debased gold coinage . The army was now seen as both an unnecessary expense and a political threat . Native troops were therefore cashiered and replaced by foreign mercenaries on specific contract . </P> <P> At the same time, the Empire was faced with new enemies . Provinces in southern Italy faced the Normans, who arrived in Italy at the beginning of the 11th century . During a period of strife between Constantinople and Rome culminating in the East - West Schism of 1054, the Normans began to advance, slowly but steadily, into Byzantine Italy . Reggio, the capital of the tagma of Calabria, was captured in 1060 by Robert Guiscard, followed by Otranto in 1068 . Bari, the main Byzantine stronghold in Apulia, was besieged in August 1068 and fell in April 1071 . The Byzantines also lost their influence over the Dalmatian coastal cities to Peter Krešimir IV of Croatia (r . 1058--1074 / 1075) in 1069 . </P> <P> The greatest disaster took place in Asia Minor, however, where the Seljuq Turks made their first explorations across the Byzantine frontier into Armenia in 1065 and 1067 . The emergency lent weight to the military aristocracy in Anatolia, who in 1068 secured the election of one of their own, Romanos Diogenes, as emperor . In the summer of 1071, Romanos undertook a massive eastern campaign to draw the Seljuks into a general engagement with the Byzantine army . At the Battle of Manzikert, Romanos suffered a surprise defeat by Sultan Alp Arslan, and he was captured . Alp Arslan treated him with respect and imposed no harsh terms on the Byzantines . In Constantinople, however, a coup put in power Michael Doukas, who soon faced the opposition of Nikephoros Bryennios and Nikephoros Botaneiates . By 1081, the Seljuks had expanded their rule over virtually the entire Anatolian plateau from Armenia in the east to Bithynia in the west, and they had founded their capital at Nicaea, just 90 kilometres (56 miles) from Constantinople . </P> <P> Manuel's death on 24 September 1180 left his 11 - year - old son Alexios II Komnenos on the throne . Alexios was highly incompetent at the office, but it was his mother, Maria of Antioch, and her Frankish background that made his regency unpopular . Eventually Andronikos I Komnenos, a grandson of Alexios I, launched a revolt against his younger relative and managed to overthrow him in a violent coup d'état . Utilizing his good looks and his immense popularity with the army, he marched on to Constantinople in August 1182, and incited a massacre of the Latins . After eliminating his potential rivals, he had himself crowned as co-emperor in September 1183; he eliminated Alexios II and even took his 12 - year - old wife Agnes of France for himself . </P>

What was the cause of the internal strife in constantinople