Stock markets around the world are plummeting after President Trump’s sweeping and unprecedented tariffs on imports to the United States took effect at midnight. They include across-the-board tariffs of 104% on Chinese goods, which prompted China to retaliate with levies of 84% on imports of U.S. goods. Hong Kong’s benchmark Hang Seng Index fell by over 13%, its biggest one-day drop since 1997. Japan’s Nikkei index fell by nearly 8%. Markets in India and the Middle East also tumbled.