What was Theodosius's
major achievement during
his reign as
emperor?

(MAJOR ACHIEVEMENT):Theodosius 1 was obliged to fight two destructive civil wars, successively defeating the usurpers Magnus Maximus in 387–388 and Eugenius in 394, though not without material cost to the power of the Empire. He issued decrees that effectively made Nicene Christianity the official state church of the Roman Empire.

Explanation: He issued decrees that effectively made Nicene Christianity the official state church of the Roman Empire. He neither prevented nor punished the destruction of prominent Hellenistic temples of classical antiquity, including the Temple of Apollo in Delphi and the Serapeum in Alexandria.

i just did something on this guy a few days a go give me two minutes to find it in my notes.