Christianity and Buddhism have a lot of similarities and difference that, such as the the time, both came to be to on how they were spread and their beliefs; just as how many Gods they believe in or even if they believe in only a God.
One of the similarities they have is their origin time. They were both originated in 6th century C.E. Even though their origin time is the same, the way they were spreaded was different. Christianity spread through the down fall of Rome, they also sent out missionaries to spread the word of their religion, beliefs, and outcomes of what will happen to the followers of the religion if they were to follow it.
However, Buddhism spread by Ashoka, a man who had lots of followers and people while he was an original Hinduism follower that switched his religion to Buddhism, who sent monks to share the teachings of the Buddha. Another similarity is that the diffusion was attributed through missionary work and conquest, that is yet another way their religion spreaded through the world.