Stocks and bond yields around the world fell Friday after President Trump threatened to impose escalating tariffs on Mexico, capping a brutal month for markets as rising trade tensions roiled investor confidence. The threat pushed stock markets down as investors feared applying tariffs on Mexican products could hurt corporate earnings, increase prices for U.S. consumers and crimp economic growth. The Dow Jones Industrial Average fell more than 300 points, while the Nasdaq Composite Index and S&P 500 both fell more than 1%. As investors sold stocks, they moved to government bonds, gold and the Japanese yen, all assets typically perceived...