In 1195, the Holy Roman Emperor Henry VI sent a man to Constantinople to demand that the Eastern Roman Emperor Isaac II pay tribute to him. Isaac II, knowing that the Eastern Roman Empire was powerless to resist the invasion of the Holy Roman Empire, had to submit to Henry VI. The Eastern Roman Empire has always regarded itself as Roman orthodoxy, so why submit to the Holy Roman Empire, the captain will tell you in detail.
First, Frederick I and Isaac II
Frederick I
In 1189, the Holy Roman Emperor Frederick I launched the Third Crusade to regain Jerusalem. The Eastern Roman Emperor Isaac II feared that Frederick I would take advantage of the opportunity to capture Constantinople, so he was very wary of him, not only refusing to supply the Crusaders, but also making small raids on the Crusaders along the way. However, Frederick I had no intention of annexing Eastern Rome, so he exercised restraint in his hostilities and sought diplomatic means to solve the problem, and frederick I negotiated with Isaac II by letter.
Isaac II
Angered by the eastern Romans' designation of him as "King of Germany" and claiming to be the true Roman Emperor, Frederick I approached Constantinople with his troops and threatened him with force. Unable to stop the crusaders from advancing eastward, Isaac II had to appeal to Frederick I, calling him "Emperor of Germany." The two sides then reconciled, and Eastern Rome allowed the Crusaders to cross their territory freely, providing supplies for the Crusaders and compensating for their losses.
Second, Holy Rome forced eastern Rome to submit
Third Crusade
In 1190, Frederick I died on the crusade and his son Henry VI became Holy Roman Emperor. Henry VI first conquered the Kingdom of Sicily in 1194 and took control of the entire Italian peninsula; then set his sights on Eastern Rome in an attempt to force it to recognize himself as the only legitimate Roman Emperor. When Frederick I went on the Third Crusade, the Holy Roman Empire recognized the weakness of Eastern Rome, so Henry VI sent an emissary to Constantinople in 1195 to demand a tribute from Isaac II.
Faced with a powerful threat from the Bulgarians and in need of assistance from the Holy Roman Empire, Isaac II succumbed to him and was willing to pay tribute to Henry VI. Soon, however, Isaac II was overthrown by his brother Alexius III and imprisoned. However, Henry VI still forced Alexius III to submit by force and promised to pay tribute to him.
Henry VI
Henry VI then planned to bring the whole of Europe to his knees and make himself a true universal emperor, but with his sudden death in 1197, the plan failed to carry out. Alexius III, aware of the strength of the Holy Roman Empire, abandoned the word "Roman" in "Roman Emperor" to indicate that he had no intention of competing with the other side.
Third, the Eastern Roman Emperor submitted to the Pope
Fourth Crusade
In 1204, the Crusaders conquered Constantinople during the Fourth Crusade, divided Eastern Rome with Venice, and established the Latin Empire and other Crusader states in the homeland of Eastern Rome. Although the monarchs of the Latin Empire adopted the title of Emperor, they called themselves "Emperor of Constantinople". But the Latin Emperor was Catholic, so he not only submitted to the Pope of Rome, but also recognized the Holy Roman Empire as the true Roman Empire, and the Holy Roman Emperor was the only legitimate Roman Emperor.
Michael VIII
In 1261, The Nicaea Emperor Michael VIII destroyed the Latin Empire and recaptured Constantinople, reviving the Eastern Roman Empire. Michael VIII then declared himself Emperor of Rome to the Holy Roman Empire and pope, with rights independent of the Church of Rome. Soon Michael VIII, recognizing the Pope's great influence over Western Europe, decided to enlist the Pope's support to avoid an invasion by King Charles I of Sicily.
From 1272 to 1274, Pope Gregory X presided over the Second Council of the Grand Dukes of Lyon. Michael VIII sent his men to the conference, recognizing the supremacy of the Pope of Rome and contributing to the unification of the Orthodox Church with the Catholic Church. Élieus X thus recognized the legitimacy of the Valleolos dynasty in ruling Constantinople, but the eastern Roman populace was generally dissatisfied with this, saying that Michael VIII had become a Frank.
The Ottomans destroyed Eastern Rome
In 1282, Michael VIII died, and his son Andronica II became Emperor of the Eastern Romans, quickly negating the unification of the Orthodox Church with the Catholic Church. The Pope of Rome was very dissatisfied with this and wanted to launch a new crusade to force Eastern Rome to submit, but was never successful. However, the rise of the Ottoman Empire at the end of the 14th century forced the Eastern Roman Emperor to turn to the Pope again to support the unification of the Orthodox Church and the Catholic Church. However, the Ottoman Empire destroyed the Eastern Roman Empire in 1453, ending the dispute between the Eastern Roman Emperor and the Holy Roman Emperor and Pope.
In general, the decline of the Eastern Roman Empire put it at a disadvantage in the struggle against the Holy Roman Empire for roman orthodoxy, forced to submit to the Holy Roman Emperor and Pope. The brief revival of Eastern Rome in the mid-13th century also failed to save it from decline, and had to seek reconciliation with the Pope again. The rise of the Ottoman Empire further forced Eastern Rome to rely on the support of the Pope and was at a disadvantage in the dispute between the two emperors until its demise.