The correct answers to this open question are the following.
The spread of Christianity in Europe and China from the viewpoint of those seeking to introduce the new religion. faced many due to the fact that people and tribes from those places already had their own belief systems, religions, or spiritual beliefs. That is why they encountered many obstacles.
The strategies they employ were that evangelizes in the 7th century when Christianity tried to spread over some regions of China, failed during the Tang Dynasty. It had to be the Jesuits in the 16th, the ones who had a little bit more of success when they introduced western education on important subjects such as science, astronomy, and mathematics.
Tribes in Europe were so difficult to convert because they already believed in their own religious teachings that included respect for mother nature and communication with the Earth, something that Christianism has never considered.
These Christian priests had successes and failures. Protestantism was better accepted in many of the European regions. However, in China, it was much more difficult for the ingrained concepts Chinese people had of Taoism or Confucianism.