The U.S. imposed an additional 50% tariff on Chinese imports on Wednesday afternoon, triggering sharp selloffs in global financial markets and forcing South Korea into emergency response mode. The tariff, which took effect at 12:01 a.m. EDT (1:01 p.m. KST), is the most severe in over a century and forms the centerpiece of U.S. President Donald Trump’s “America First” trade doctrine. China responded Wednesday evening by announcing it would raise tariffs on select U.S. imports from 34% to 84%, effective April 10. Concurrently, the European Commission also announcedthat EU Member States had unanimously approved trade countermeasures against the U.S.