NEW YORK—Buoyed by positive news from the war front, the Dow Jones Industrial Average soared more than 300 points Monday after the killing of more than 400 Republican Guard soldiers near the northern Iraqi town of Mosul. "These deaths have really boosted investor optimism and confidence," New York Stock Exchange chairman Dick Grasso said. "Before this, we'd tried lowering interest rates, lowering taxes, and all sorts of other things to jump-start the market, but nothing worked. Lowering the population of Iraq finally seems to be doing the trick."