The automotive industry is one of the most influenced by the Chinese policy of promoting Chinese business over foreign.
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For years, there were requirements to set up joint ventures with Chinese companies (at least 50% share) to produce and sell cars in China, which for foreign manufacturers could mean loss of control over technology.
On the other hand, a 25% import tax on cars prevented competition through import. There were also other policies like subsidies for New Energy Vehicles (only with batteries produced locally) and more.
The recent move made by President Trump (who heard Elon Musk's complaints) is kind of an answer to the general disproportion of how businesses are treated in China and the U.S. (not only automotive ones).
The Chinese government recently hinted at lowering tariffs for foreign cars and also reducing requirements for the joint ventures. It would enable Tesla to sell more cars in China and even build a new factory there. It seems that Elon Musk is happy with this.
We will see whether or not there really will be positive progress or if the tariff war will expand in the coming days.