TikTok vs Douyin: why does China have its own TikTok?

We're digging deep into China's version of TikTok called Douyin. How different is Douyin from its international version TikTok? Why are there two almost-identical apps out there? And how are Chinese people using Douyin differently from users of TikTok? To truly understand Douyin, we attended a weekend class that costs about US$1,400 in Shenzhen, China, about how to get rich on the app.