Because it was growing more and more popular and more people were becoming Christians.
There are 5 main reasons why the US joined World War 1 I don't know which reasons you have already listed so I'm just gonna say all 5 the 1st one would be German atrocities in Belgium 2nd would be economic interests 3rd would be sinking of the Lusitania the 4th of the unrestricted submarine warfare and the 5th would be the zinmerman telegram
One factor that helped Buddhism spread to China was the way of the Silk Road.
