How did Constantine become sole ruler of the Roman Empire in 324 CE?

Constantine became the sole ruler of the Roman Empire in 324 CE by defeating his final rival, Licinius, in a decisive military campaign.12

Following the defeat of Maxentius at the Battle of the Milvian Bridge in 312 CE, Constantine had secured control over the Western Empire, while Licinius ruled the East. Although the two initially maintained an outward alliance—marked by the Edict of Milan in 313 CE—tensions over power and religious policy eventually led to open conflict.3241

After an initial clash in 316 CE resulted in territorial losses for Licinius, a decade of uneasy truce followed. In 324 CE, war erupted once again. Constantine routed Licinius at the battles of Adrianople and Chrysopolis. Following his surrender, Licinius was executed, leaving Constantine as the undisputed and sole emperor of the entire Roman Empire. He subsequently solidified his legacy by founding Constantinople as the new administrative capital.125