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The answer is A: Constantine recognized the legality of Christianity. This was the biggest change in the Roman Empire to date. Constantine had a change of heart due to a dream he was seen by Jesus- and that is the result he became Christian. In addition, 'the great schism' was a barrier that Constantine and pope were separated (both which they agreed on) due to different ethnicities, languages & culture.
The great schism chart
Constantine's side
East side- middle easterners, Egyptians, turkey
Languages- turkish, Arabica
Pope's side
West side- Rome, Italy
Language- Latin
C the growth of support and segregation
If you've been assigned a research paper on the Holy Wars, then an "Encyclopedia" would provide a factual base for additional research, since it is the most reliable.