Ever since the the Anastasian War ended in 506, the Byzantine and Persian governments had fought over control of Iberia, and Mesopotamia in general. The ever more imposing Byzantines began trying to make advances into the territory, but the Sassanids stopped them. Along with this was a succession crisis in Persia, as Kavadh of Persia asked for Justin I to adopt his son, Khosaru, who was threatened by his brother, Mazdakite. Justinian, Justin's nephew, supported the move, but Justin's Quaestor, Proculus, and Justin eventually denied the adoption. Although negotiations broke down and war was declared in 526, full war didn't start until 530. But Persia first invaded Iberia in 528, and the King of Iberia, Gourgen, asked for Byzantine help.
Belisarius lead a Byzantine army into Iberia, taking over most of the north in a few months, when the Persians began launching a counterattack against the Byzantines. Raids into the Persian homeland forced the Persian to withdraw a small number of troops from the front in order to defend Persia, but not the number Belisarius wanted. At Dara in 530, a Byzantine force of 25,000 against 50,000 Persians, winning a powerful, yet indecisive victory. At the Battle of Satala a few month later, again with similar conditions, the Byzantines also won, but still decisive victory eluded them, and the two sides continued to fight. Multiple small skirmishes occurred between the two sides afterwards., but a decisive battle eluded both sides, until 531.
Battle of Callinicum
At the Battle of Callinicum, on April 19, 531, the Byzantines engaged the Persians, and the two sides stood in a stalemate until the Persians attacked the Byzantine right flank. But Belisarius' leadership allowed for his men to stand firm against the Persians, and the Byzantines counterattacked. The Byzantines followed the Persians as they retreated back into Persia, and the Byzantines invaded Persia in late 531, capturing most of the eastern border, and forcing the Persians into a humiliating peace in 532.
The "Eternal Peace" agreement made between the two countries was signed by, now emperor, Justinian I and Kavadh I of Persia. King Gourgen agreed to have Iberia annexed into the Byzantine Empire, and Persia was forced to give up the land it had lost to Belisarius' invasion to the Byzantines.