Assume the world consists of two countries, China and the US. If China decides to stimulate growth through a policy of running a large export trade surplus, why does the US have to run a trade deficit...

Assume the world consists of two countries, China and the US. If China decides to stimulate growth through a policy of running a large export trade surplus, why does the US have to run a trade deficit and a net capital account deficit? What is in the impact on US national income and employment?