His successor was Basil II, who may have poisoned him. Basil was the son of Romanus II, and was not a proven general or a member of the Anatolian aristocracy, as had been Nicephorus Phocas and John Tzimisces. As a result, he had tremendous difficulty suppressing revolts and challenges to his throne. The effort to establish his throne took eleven years, and culminated with resort to Vladimir of Rus, Sviatoslav's son. In return for the Emperor's sister's hand in marriage, Vladimir provided 6,000 Varangian warriors. In 989, Basil was able to finally meet his chief nemesis, Bardas Phocas, whose forces were ultimately destroyed. The latter challenged Basil to a duel, but died of a stroke in the midst of his own charge. By 989, then, Basil had outfought his internal opponents, and had stewarded over Vladimir's marriage to Princess Anna, as well as Vladimir's entry into the Orthodox Christian fold, an event with tremendous cultural significance. From 990, Basil was able to concentrate on three things: 1) punishing and destroying of the re-emergent Bulgar state; 2) further securing of the Eastern border; and 3) clipping the wings of the Anatolian aristocracy and reinvigorating of the Theme armies' demographic basis.
During the years of civil unrest in Byzantium, a certain Samuel had proclaimed himself Bulgar Czar. Starting from 980, he invaded Thessaly every year, in 986 capturing its capital Larissa. Basil countered by leading an army in person to meet Samuel. He was ambushed by the Bulgars, however, at Trajan's gate pass, and lost most of his forces. In 991, Basil returned to discipline the Bulgars definitively. Through 995, Basil's forces ranged through Thessaly. Though not winning any shocking victories, the methodical advances, rigorous discipline and planning, and careful precautions brought several cities and regions back to Byzantium. Forced to fight in the East for the next few years, Basil saw to the increased prestige and power of his client the Republic of Venice. It was now to guard the Dalmatian coast and protect the Greek-speaking cities from Samuel. From 1000-1014, Basil II undertook continuous campaigns in the Eastern Balkans. Advancing the whole time, in 1014, there was a momentous battle, at the narrow passes of Cimbalongus near the upper Struma River. The Bulgars were surprised and annihilated, with 15,000 taken prisoner. In an act earning him the name Bulgar-Slayer, or Bulgaroctonus, Basil sent these prisoners home in groups of 100--ninety-nine of each group were blinded, while their leader was left with one eye to guide them. Czar Samuel died upon seeing his returning army. In 1018, the Bulgars were finally eliminated as a political entity, and Basil personally occupied their capital. The entirety of the Balkan Peninsula was once more Byzantine.
Basil's activities in the East were mostly defensive. In 995, the Fatimids put Aleppo under siege. It was now a Byzantine protectorate, so its amir appealed to Basil. Putting his entire army on mule-back, Basil rushed to Aleppo's defense. The Fatimids were defeated, and fled back to Damascus. To drive home his superiority, Basil sacked Emesa, and raided as far south as Tripoli before heading back west to face Bulgar issues. Returning to the region in 1023, he established eight new Themes, continuing northeast of Antioch. Byzantine dominance stretched to Azerbayjan, and at his death in 1025, Basil was planning an invasion of Sicily. One group was glad of his death. While in the east in 990-s, Basil was angered by the degree of large landholder control in the area. Their estates had expanded both onto imperial lands as well as onto the local village communes--those centers on which Theme soldiers depended for support. Thus, while individual Byzantine elites, and even generals, were enriched, the state and army ran the risk of impoverishment. On January 1, 996, Basil decreed that for a claim to land to be valid, it had to go back to Romanus I Lecapanus, sixty-one years before. Thus, much of the Anatolian aristocracy were immediately deprived of their lands--the Phocas family, having produced Nicephorus the emperor, lost almost all their estates, while other families were reduced to beggary. The peasants, and small holders, however, were now empowered to regain lost lands. When Basil died and his inadequate brother Constantine VIII became emperor, the land laws were forgotten. The Anatolian landholders reacquired their properties, and the region returned to a country of estates, with the Theme armies damaged, and tax revenues lessened.
With Constantine, the Byzantine decline begins. Constantine was of no use to the empire. Aside from ending a regulation requiring the Anatolian and Constantinople Aristocrats to pay the peasants' tax arrears, he bequeathed the empire to his daughter Zoe, who came to rule in 1028, sharing the Imperial crown with a series of non-entity emperors for the next thirty years. Capital and provincial elites manipulated the sovereigns. Romanus III ended the laws protecting Asia Minor peasants before being killed on Zoe's orders. The military began to lose numerical strength. One of Romanus' murderers became her co-emperor as Michael IV. An epileptic, he began gross financial mismanagement. Under Romanus, the number of government jobs increased as a means for aristocratic self-aggrandizement. This meant that state funds became scarce. Michael responded by farming out the taxes, which had with harsh consequences for the non-elite tax-payers, and debased the coinage, which caused mounting hording and decreased buying power for those on inelastic incomes. In 1041, Constantine IX Monomachus became Emperor. Fearing for Byzantium's declining military posture, important generals attempted a coup. Monomachus barely survived, and, as a result, took an aggressively negative approach to the army. He starved it for funds and man-power, allowing peasants to buy their way out. The old Byzantine army based on Theme soldiers and officers rising through the ranks and long years of training disappeared; emperors came to rely on foreign mercenaries of doubtful loyalty. Thus, between 1040 and the late 1060s, the civil aristocracy of Constantinople saw to the demilitarization of the Empire, while Asia Minor elites focused on increasing their holdings.
By the late 1050s, though, the eastern frontier was newly threatened. Muslim Turks had been migrating through the Islamic World from Iran westwards since the early 1000s. A Turkic Islamic state ruled by the Seljuk dynasty had occupied Baghdad in 1040s, and offshoots of it, as well as less disciplined, semi-nomadic Turcoman tribes, had begun incursions into Byzantine lands from the mid 1060s. The leaders in Constantinople belatedly realized that they had to strengthen their eastern defenses, and consented to the ascent of a military leader as emperor. Romanus IV Diogenes came to power in 1068, and gathered a mercenary army of Bulgars, Franks, Normans and others. He took it east to garrison the forts, but was ambushed in east-central Anatolia by Seljuk forces under Alp Arslan. The Byzantine forces were totally defeated. Romanus himself was taken into captivity, where he died. There was absolutely no Anatolian Byzantine army, and Turcoman tribesmen ranged freely and widely in Eastern and Central Anatolia for the rest of the century and beyond.
Byzantium had seemed a self-sustaining entity beginning in the late 700s. What is conspicuous about the period from 950-1025 is that the Empire could make such strides forward while still hemmed in by opponents on all sides, including a Latin West increasingly disassociated from it culturally, religiously, and politically. What conditions, in short, allowed the tremendous successes of Nicephorus Phocas and John Tzimisces? Political elites at the center were no more unified than before, and imperial reigns were short, until the period of Basil II. As usual, some of the reasons are internal, while much involves the disposition of Byzantium's neighbors. Internally speaking, Byzantium had at no time lost the far-ranging trade connections going as far north as Russia and as far east as Central Asia. This permitted the state to enjoy a wealth that Western polities could not yet imagine. Also, in spite of the enervating struggles at the center among generals and emperors, the civil-military bureaucracy of the middle echelons was well established, professional, and continually loyal to the state and regime as a whole, as an incarnation of a specifically Christian civilization. On the provincial level, the Theme armies were also maintained during this period, though in the 970s the Anatolian aristocracy began to undercut their demographic and agricultural basis. Still, what emerges is a pattern of a healthy Theme system providing imperial strength, as long as the creeping Anatolian aristocracy's annexations were kept at bay. Even these latter were often able to provide military muscle, and several brilliant generals came from their ranks, such as the Phocas brothers, Sclerus, and Tzimisces.