Mission and culture
One of the things that shocked, or at least surprised me when I began to study missiology was how many missiologists were ignorant of history. They spoke of cross-cultural mission and inculturation and things like that, but in an ahistorical way.
I wrote an essay giving Boniface of Crediton as an example of Christian missionaries going to people of a similar culture to their own, and the lecturer, a well-known and widely respected missiologist, queried this, and was highly sceptical. The fact is, however, that within a generation or two of beoming Christian themselves, the English were sending missionaries to their still-pagan cousins back in Germany, where their own ancestors had come from. They were not going to people who spoke a foreign language, or people whose culture was totally different. The English had been Germans more recently than Americans have been English today.