The US & EU is with the World Trade Organisation, WTO HQ in Geneva. China was invited to join, on favourable terms, which is why we are now flooded with Chinese products in almost every sector. The EU has an agreement indirectly with China.
Friends or allies make trade deals and agree on many things. Britain, as part of the EU, has these arrangements in place. If Britain leaves the EU, much will have to be put in place again.

I watched half the video, I thought it was sensational journalism. Good night!