Question

What did Constantine do to help reunite the empire?

He made Christianity the sole religion, to unite everyone.
He cut the size of the empire to make it more manageable.
He moved the capital to a better location for defense and trade.
He forced all Roman citizens to pledge allegiance to him.

Answer 1

Found this off of google, "Constantine now became the Western Roman emperor. He soon used his power to address the status of Christians, issuing the Edict of Milan in 313. This proclamation legalized Christianity and allowed for freedom of worship throughout the empire. ... In 324, Constantine defeated Licinius and took control of a reunited empire."

So, the answer to your question is D)He made Christianity the sole religion, to unite everyone.

Hope this helps have a great day and stay safe! :) :D :3

Also sorry I was late with the answer.