Battle of Adrianople: Emperors Constantine the Great and Licinius fight a Roman civil war. This is the second between these two emperors, and as with the first, it ends with Constantine defeating Licinius.
The previous conflict produced a peace treaty that was favorable to Constantine, but over the past ten years he has been looking for any excuse to resurrect the war and eliminate Licinius once and for all.
At first Constantine spares Licinius' life because he's married to Constantine's sister, Constantia, but within a year he'll be executed. At no point does he even try to spare Licinius' reputation — on the contrary, he goes on the offensive to make his rival look as bad as possible.
In particular, he'll have Licinius portrayed as a violent pagan supporter, a claim that's patently false. Licinius signed the Edict of Milan with Constantine, ending the persecution of Christians. It's possible that Licinius even converted to Christianity himself at some point.
None of this is relevant to Constantine, though, nor is it relevant to church leaders he has supporting him. Eusebius of Caesarea will participate in the smears against Licinius, serving the interests of his political master rather than the interest of truth.