Mainly reason, logic and good sense.
People. People who didn't want things to change who were afraid of following another faith simply just people.
The Byzantines spread Orthodox Christianity to those areas.
He ended the persecution of Christians
They were financed to do so...it was a way of colonizing California and they believed that by converting Indians to Christianity they were saving their souls.
Prince Henry the Navigator hoped to spread Christianity through the exploration and colonization of new lands, particularly in Africa. He saw this as a way to expand Christianity and gain converts to the faith.
The Nestorians spread Christianity all the way across central Asia, reaching China by 635 CE. Political events in China and Mongolia, as well as the rise of Islam, reversed this.
Christianity and Islam spread far from where they were founded
they wanted to and its none of your dang biz
The Roman Roads effected early Christianity by the way it was spread. Paul had to spread the word of Christianity by traveling to different places. At this time and moment in past, all roads lead back to Rome. So naturally it didn't effect much except for the fact that Paul didn't have much trouble finding his way back. He spread the word to many families about Jesus and God's teachings. Almost instantly they became followers. Without these roads, Paul wouldn't have been able to spread the faith of this new belief!
We do not know how or when Christianity first arrived in Rome, but Paul's Epistle to the Romans demonstrates a flourishing Christian community existed there when he proposed his visit to Rome, on his way to Spain.
Philippines were introduced to western paintings by the Spaniards in the 16th century. The paintings were used as a way to spread Christianity to the Philippines.
The Christians told people about their faith, and the converts spread the word, and eventually made their way to Rome, where they kept growing until Constantine made Christianity the country's religion.