Britain's American colonies broke with the mother country in 1776 and were recognized as the new nation of the United States of America following the Treaty of Paris in 1783. Buoyed by victories in World Wars I and II and the end of the Cold War in 1991, the US remains the world's most powerful nation state. The US has the largest and most technologically powerful economy in the world, with a per capita GDP of $43,500. In this market-oriented economy, private individuals and business firms make most of the decisions, and the federal and state governments buy needed goods and services predominantly in the private marketplace. The onrush of technology largely explains the gradual development of a "two-tier labor market" in which those at the bottom lack the education and the professional/technical skills of those at the top and, more and more, fail to get comparable pay raises, health insurance coverage, and other benefits. Since 1975, practically all the gains in household income have gone to the top 20% of households. The response to the terrorist attacks of 11 September 2001 showed the remarkable resilience of the economy. The war in March-April 2003 between a US-led coalition and Iraq, and the subsequent occupation of Iraq, required major shifts in national resources to the military. The rise in GDP in 2004-06 was undergirded by substantial gains in labor productivity. Hurricane Katrina caused extensive damage in the Gulf Coast region in August 2005, but had a small impact on overall GDP growth for the year. Soaring oil prices in 2005 and 2006 threatened inflation and unemployment, yet the economy continued to grow through year-end 2006. Imported oil accounts for about two-thirds of US consumption. Long-term problems include inadequate investment in economic infrastructure, rapidly rising medical and pension costs of an aging population, sizable trade and budget deficits, and stagnation of family income in the lower economic groups. The merchandise trade deficit reached a record $750 billion in 2006.