My question would be what exactly did Christianity bring to the table that wasn't already there?
It was this New Covenant brand of love that began to change the world. The citizens of the Roman Empire began to internalize this and embrace it. The empire began to change and then the world began to change. Something that was unprecedented happened. Something that had never happened before happened.
In his book, ‘The Triumph of Christianity’, Bart Ehrman…a world renowned New Testament manuscript scholar, but also an atheist…said, “Christianity not only took over an empire, it radically altered the lives of those living in it. It opened the door to public policies and institutions to tend to the poor, the weak, the sick, and the outcast as deserving members of society. It was a revolution that affected government practices, legislation, art, literature, music, philosophy, and—on the even more fundamental level—the very understanding of billions of people about what it means to be human. However one evaluates the merits of the case, whether the Christianization of the West was a triumph to be treasured or a defeat to be lamented, no one can deny it was the most monumental cultural transformation our world has ever seen.”