There was no empire-wide persecution of Christians until the reign of Decius in the third century. ... With the passage in AD 313 of the Edict of Milan, in which the Roman Emperors Constantine the Great and Licinius legalised the Christian religion, persecution of Christians by the Roman state ceased.
Because when people charged from the trench they were most likely killed in what is called no mans land.Trench warfare resulted in little territorial gain
