Final answer:
China has some of the highest barriers to the diffusion of new religions due to severe restrictions and government control.
Step-by-step explanation:
The country that has some of the highest barriers to the diffusion of new religions in the modern era is China. In China, religious groups have been subjected to severe restrictions, including banning worship services and prohibiting the display of non-Islamic religious symbols. The government in China considers religious practices to be detrimental to its communist goals and often imposes limitations to control the spread of new religions.