<P> From its emergence as an independent nation, the United States has encouraged science and innovation . In the early 20th century, the research developed through informal cooperation between U.S. industry and academia grew rapidly and by the late 1930s exceeded the size of that taking place in Britain (although the quality of U.S. research was not yet on par with British and German research at the time). After World War II, federal spending on defense R&D and antitrust policy played a significant role in U.S. innovation . </P> <P> The United States is rich in mineral resources and fertile farm soil, and it is fortunate to have a moderate climate . It also has extensive coastlines on both the Atlantic and Pacific Oceans, as well as on the Gulf of Mexico . Rivers flow from far within the continent and the Great Lakes--five large, inland lakes along the U.S. border with Canada--provide additional shipping access . These extensive waterways have helped shape the country's economic growth over the years and helped bind America's 50 individual states together in a single economic unit . </P> <P> The number of workers and, more importantly, their productivity help determine the health of the U.S. economy . Consumer spending in the U.S. rose to about 62% of GDP in 1960, where it stayed until about 1981, and has since risen to 71% in 2013 . Throughout its history, the United States has experienced steady growth in the labor force, a phenomenon that is both cause and effect of almost constant economic expansion . Until shortly after World War I, most workers were immigrants from Europe, their immediate descendants, or African Americans who were mostly slaves taken from Africa, or their descendants . </P> <P> Beginning in the late 20th century, many Latin Americans immigrated, followed by large numbers of Asians after the removal of nation - origin based immigration quotas . The promise of high wages brings many highly skilled workers from around the world to the United States, as well as millions of illegal immigrants seeking work in the informal economy . Over 13 million people officially entered the United States during the 1990s alone . </P>

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