U.S. stock prices fell sharply Monday,following conflicts in the Middle East, and weaker economies in China and in Europe.U.S. stocks started the new year with the most selling of stocks and investments since September 2015,reported CBS News.Stocks lost between 2 percent and 3 percent in trading.The weaker economy in China "reignited fears of a global slowdown," according to Reuters.Chinese stocks fell about 7 percent Monday.This caused officials to halt trading for the dayto stop the falls on the Shanghai and Shenzhen exchanges.It was the first time China used a "circuit breaker," said CBS News.A "circuit breaker" in a stock exchange stops trading that happenswhen investors panic and sell too much in too short a time.Reports showed that Chinese manufacturers are not producing as much as before.Investors say China's economic growth is slowing.China is the world's second-largest economy and a key market for many other nations.Japan's Nikkei index was down 3 percent,and Hong Kong's Hang Seng index fell more than 2 1/2 percent by the close of trading.European markets followed Asia's lead.Germany's stock market was down more than 4 percent.The British stock market fell by more than 2 percent.Meanwhile, crude oil prices increased.Analysts are concerned that tension between oil producersSaudi Arabia and Iran might reduce energy supplies.