Assets held by life insurers back the companies' life, annuity, and health liabilities. Accumulating these assets, via the collection of premiums from policyholders and earnings on investments, provides the U.S. economy with a important source of investment capital. Life insurers have invested $4 trillion invested in the U.S. economy, including $1.2 trillion in new net investments in the five-year period between 2002 and 2006. Life insurers are the largest source of bond financing for corporate America, and have been since the 1930s, with $1.9 trillion invested in 2006. At the end of 2006, life insurers held over $579 billion in government bonds, which help fund urban renewal and support America's infrastructure. The industry holds about $314 billion in commercial mortgages and provided $58 billion in new financing to the commercial mortgage market in 2005.