How did christianity spread through western and central europe during the early middle ages?
missionaries traveled across the continent, preaching the gospels.
the gospels were translated into latin, the language peasants used.
the benedictine rule forced everyone to pay a tithe to support new churches,
monasteries provided education and care for the poor.

Christianity continued to spread because of many missionaries going out and Spreading the word of God. One other reason would have to be the spread of Catholicism which was Christianity but, later changed because of the Romans. This is my basic Knowledge but, I'm not sure if this is going to help but, here you go.

Explanation:

Missionaries traveled across the continent, preaching the Gospels.

the fact that could also be added to column b is that during world war ii, specifically between the years 1941 and 1945, japan expanded its territory towards the indonesian territory in what was known later as part of the "pacific war". in that time, japan could conquer the philipines, singapore,   borneo, central java, malang, cebu, sumatra and various other islands of the area, therefore expanding its territory for a brief period of time.

the iconic cartoon that you are talking about is probably a man standing on top of a country with his legs spread wide. 

this cartoon suggests that europeans are powerful enough to subdue an entire continent. this was a satirical image that was drawn during the time of the colonization of the british empire in africa.

this image was inspired by the plans of the british empire to create telegraph lines all over africa promoting the further spread of its colonies through faster communication. the picture depicts the colonial mentality of the british empire in general as well as the struggle of africans to claim their own land. hope this ! (: