Long ago, a man named Muhammad claimed to have received a vision from Gabriel, informing him that he was to be God’s messenger, consequently spreading the word of what would be known as the religion of Islam. Islam, at first, grew slowly; however it would soon become one of the largest beliefs, as Muslims - partisans of Islam - would endeavor to conquer new lands. These conquests came to be known as the Arab Muslim Conquests (also Islamic Conquests/Arab Conquests). One certain location which experienced great loss was Byzantium (Byzantine), part of the Roman Empire.
The Islamic Conquests were begun by the Rashidun, the four Rightly Guided Caliphs, and were the cause of the massive spreading of Islam throughout the Mediterranean and European territories. The conflict between Byzantium and the Muslims is known as the Byzantine-Arab Wars. Byzantium was an empire, appropriately called the Byzantine Empire, whose capital of Constantinople was located on the Bosporus. The Byzantine Empire is another title to represent the Eastern half of the Roman Empire.
Previous to the initial conflict between the Muslims and the Byzantine Empire there was separate, lasting conflict between Byzantium and Persia (under the Sassanid dynasty). This conflict is often claimed to be the cause of Byzantium's incompetence to resist the Islamic force, as Byzantium resources were drained. The emperor of Byzantium was Heraclius at the time of the opening conflict, and at the head of the Islamic force was the Prophet Muhammad. Although the territory dominated by the Byzantium Empire was not completely taken by Muslim force, much of it was taken into the possession of Islam.
The Byzantium-Muslim Wars were long lasting, as the initial conflict prevailed from 634 - 717. Major conflicts of the wars included the First and Second Arab Sieges of Constantinople, in which naval, defensive, and land forces were ensued against one another; and as the Muslim force attempted to take Constantinople, the Byzantine armies attempted to hold their own, in retaliation to growing Islam. Throughout the lengthy struggle many caliphs continued to fight against Byzantium, retaining loyalty to Islamic faith. In correlation with the lengthiness of the war, long lasting effects persisted for both Arab and Byzantine provinces. Africa and the Middle East were claimed by the Arabs, leaving the Byzantine Empire with very significant loss of territory.
Gordon, Matthew. The Rise of Islam. Greenwood Publishing, 2005.Kaegi, Walter Emil. Byzantium and the Early Islamic Conquests. Cambridge University Press, 1992.