What’s behind US export controls on technology to China?

US President Joe Biden has imposed sweeping controls on exports of semiconductors to China. Also known as ‘semis’ or ‘chips’, semiconductors are needed to run nearly all electronics. American companies will be restricted from selling advanced chips to China, and supplying Chinese firms with tools to make their own. China has accused the US of weaponising technology. What’s behind Biden’s decision? And how much is down to politics?