Kingdom of Byzantium

History of the Byzantium
In 293 AD, Emperor Diocletian created a new administrative system (the tetrarchy), to guarantee security in all endangered regions of his Empire. He associated himself with a co-emperor (Augustus), and each co-emperor then adopted a young colleague given the title of Caesar, to share in their rule and eventually to succeed the senior partner. Each tetrarch was in charge of a part of the Empire. In 330 AD, Constantine I moved the seat of the Roman Capital to Constantinople and then made the state religion Greek-Orthodox-Christianity. The Empire would be at its peak when Justinian I in the mid 6th century brought the empire to its largest extent since the original Roman Empire. During the 4th Crusade, the Byzantine pretender Alexios IV Angelos was dead, thus never promising riches to the crusaders to invade Constantinople. Without this key event, Constantinople was not sacked. The Byzantine idea was kept alive for a couple more centuries till time finally caught up and Ottomans take over. Then on March 25, 1821, the Kingdom of Greece formed from the dying Ottoman Empire. The King of Greece would be the deposed Byzantine Dynasty of Palailogos. After WW1 the Kingdom of Greece achieves the Megali Idea and takes former Byzantine territory, including Cyprus. This acquisition of territory and the coveted city of Constantinople allowed for the Kingdom of Greece to claim the title of Byzantium, and by extension Rome. After WW2 Byzantium looses land in Anatolia but gains territory in North Macedonia and some of Southern Bulgaria land.

Modern Day Byzantium
(I'll to this later)