Constantine V vs Mongke Temur

Constantine V convened the Council of Hieria, which formally condemned the veneration of icons as idolatry. This council established iconoclasm as official Byzantine Church doctrine, intensifying the religious controversy that divided the empire.

Following the Council of Hieria, Constantine V intensified persecution of icon venerators. Monks were imprisoned, executed, or forced to marry. Monasteries were confiscated and converted to barracks or secular use. This policy deepened the iconoclast schism.

Constantine V led nine major campaigns against the Bulgarian Empire, achieving several victories including the Battle of Marcellae (759) and the Battle of Anchialus (763). These campaigns temporarily weakened Bulgaria but did not destroy it.

Constantine V oversaw the restoration of the Aqueduct of Valens, which had been damaged by the Avars. The repaired aqueduct restored water supply to Constantinople, improving urban infrastructure and public health.

Constantine V died while on campaign against the Bulgars. His death occurred during a military expedition, and he was succeeded by his son Leo IV. His campaigns had temporarily checked Bulgarian expansion but left the empire exhausted.

Mongke Temur, as Khan of the Golden Horde, refused to attend the kurultai called by Kublai Khan and ceased sending tribute to the Mongol Yuan dynasty. This act effectively declared the Golden Horde's independence from the central Mongol Empire.

Mongke Temur launched a military campaign against the Ilkhanate, the Mongol state in Persia, over control of the Caucasus region. The war resulted in a stalemate but solidified the Golden Horde's position as a rival power.

Mongke Temur formed an alliance with Byzantine Emperor Michael VIII Palaiologos, sealed by a marriage between a Mongol princess and a Byzantine noble. This alliance strengthened trade and diplomatic ties between the Golden Horde and the Byzantine Empire.