China has banned the export of rare but critical earth minerals used in the manufacture of important semiconductors to the United States in the latest move in an ongoing tech war between the two superpowers. Beijing's announcement on Tuesday came just one day after the US ramped up restrictions on the export of advanced chips to China, which affects the country's ability to develop advanced weapons systems and artificial intelligence. So why is a "tech war" brewing between China and the US, and why does it matter? For months, the two countries have been involved in tit-for-tat export restrictions. The US hopes to cripple China's military and artificial intelligence (AI) advances as well as hamper its ambitions to become a global leader in clean energy and other technologies.

China has been on the receiving end of semiconductor export restrictions for years. On July 3, the Chinese Ministry of Commerce announced that the export of gallium and germanium, two elements used in producing chips, solar panels, and fiber optics, will soon be heavily restricted. Exports of the materials will need to be approved by the government, and Western companies that rely on them could have a hard time securing a supply. Even though the news immediately sent the price of gallium and germanium up, the curbs are not likely to hit the US as hard as American export restrictions have hit China. Zeyi Yang, our China reporter, explains why.