U.S.-China economic ties have expanded substantially over the past three decades. Total U.S.- China trade rose from $2 billion in 1979 to $562 billion in 2013. China is currently the United States' second-largest trading partner, its third-largest export market, and its biggest source of imports. China is estimated to be a $300 billion market for U.S. firms (based on U.S. exports to China and sales by U.S.-invested firms in China). Many U.S. firms view participation in China's market as critical to staying globally competitive. General Motors (GM), for example, which has invested heavily in China, sold more cars in China than in the United States each year from 2010 to 2013. In addition, U.S. imports of low-cost goods from China greatly benefit U.S. consumers, and U.S. firms that use China as the final point of assembly for their products, or use Chinesemade inputs for production in the United States, are able to lower costs. China is the largest foreign holder of U.S. Treasury securities (nearly $1.3 trillion as of April 2014). China's purchases of U.S. government debt help keep U.S. interest rates low.