Following Galerius' recognition of Constantine as emperor, Constantine's portrait was brought to Rome, as was customary. Maxentius mocked the portrait's subject as the son of a harlot, and lamented his own powerlessness.
http://en.wikipedia.org/wiki/Constantine_the_Great#cite_note-83 Maxentius, jealous of Constantine's authority,
http://en.wikipedia.org/wiki/Constantine_the_Great#cite_note-84 seized the title of emperor on 28 October 306. Galerius refused to recognize him, but failed to unseat him. Galerius sent Severus against Maxentius, but during the campaign, Severus' armies, previously under command of Maxentius's father Maximian, defected, and Severus was seized and imprisoned.
http://en.wikipedia.org/wiki/Constantine_the_Great#cite_note-85 Maximian, brought out of retirement by his son's rebellion, left for Gaul to confer with Constantine in late 307.
WI Galerius (who was frustrated by Constantine's proclamation as Augustus in 305) instead of refusing the title to Maxentius allied with him granted him recognition in a move to weaken Constantine's powers and drag him to war?
How is this altering History? Any thoughts?