The Beginning of Byzantine Empire
The Byzantine Empire began as a Roman Empire splinter called Byzantium, which was founded by Constantine the Great.
Constantine was born in Dalmatia, in what is now Croatia. He became emperor at age 20 and ruled from 306 to 337 AD. His region saw three major achievements; he converted to Christianity; he built Constantinople as his new capital city; and he established Christianity as the official religion of Rome (which meant that all people would have to follow this one faith).
However, the eastern and western Christianity separated in the Great Schism in 1054. This event was caused by a disagreement over the authority of the papacy. The eastern church rejected the pope's claim to universal jurisdiction, while the west continued to recognize him as the head of their church. This led to years of conflict between East and West that culminated in 1453 when Constantinople fell to invading Islamic armies.
The Great Schism led both churches down different paths: while most Eastern Christians continued practicing their religion without any significant changes in doctrine or liturgy. Western Christians adopted many new doctrines through reform movements like Martin Luther's Reformation (1517-1648).
The Peaks of Byzantine Empire
The Byzantine Empire’s peak came under Justinian I (r. 527-565) when he reconquered territory western Europe and North Africa. He also expanded the borders of the empire, bringing it to its greatest extent ever by 715 AD. This expansion was made possible by a powerful army that could fight on multiple fronts simultaneously - an advantage that would prove crucial later on during the Muslim invasions of Constantinople in 673-74 and 717-18 CE. When Arab armies crossed over into Anatolia from lands across Asia Minor territory before marching into northern Syria from Palestine via Antiochia ad Orontem (modern Antakya).
In fact, it was this threat from outside forces that led Emperor Heraclius to turn his attention towards stabilizing Europe rather than continuing eastward toward Persia or India; he did not want another civil war like what happened with Constantine after he had forced Arianism upon Nicene Christianity instead opting for compromise within their faith communities without being persecuted by other sects or factions within society.
During the iconoclastic period, icons were banned and destroyed as they were viewed as idolatry to false gods. Iconoclasts were people who believed that religious icons were idolatry. The iconoclastic movement began in the 7th century and continued until 9th century with some periods of intense persecution by both Christians and Muslims alike.
After losing its Italian territory to Charlemagne's Holy Roman Empire, the Byzantine Empire declined from being a regional power to a regional player by the end of the 11th century. The loss of Italy forced Byzantium to turn inward and focus on its eastern provinces. By this time, most of what was once known as "Byzantine" had been absorbed into other empires or adopted by them (most notably Islam).
The Union of Lyons and Florence in 1439 was a major step forward for the Byzantine Empire, as it reunited with Rome and ended the schism between them. However, this union wasn't fully realized due to another schism caused by Pope Eugene IV (1431-1447). Eugene refused to recognize any agreements made between Byzantine Emperor Constantine VIII Paleologus (1341-1391) and his brother John VI Cantacuzenos (1347-1354), so he severed relations with both countries until they could make up their differences in earnest.
The Byzantine Empire had a long history of both ups and downs. This is evident in its history, which includes many instances of success as well as failure. The Byzantine were one of the greatest empires ever to exist on earth; the ruled over much of Europe, Asia Minor (modern Turkey), North Africa and parts of Syria for nearly 1,000 years until they were defeated by Turks at the Battle of Manzikert in 1071 AD.