“To succeed in the U.S. economy, companies must constantly adapt to changing conditions. Though some of the nation’s largest corporations — companies such as General Electric, Exxon Mobil, and Walmart — have always dominated, for many American consumers the landscape of companies has shifted over the course of their lifetimes. Though industrial companies used to be among the largest in terms of revenue, in the more modern era internet and tech giants like Google, Apple, and Amazon, are decisively making their way toward the top of the list. 24/7 Wall St. reviewed annual revenue figures for the nation’s largest 500 companies in each year from 1955 to 2016 — figures came from business magazine Fortune. General Motors was the nation’s largest company throughout the 1950s, ‘60s, and part of the ‘70s. Exxon Mobil edged out the automaker in 1975, but GM returned to the No. 1 position periodically in subsequent years. Since 2001, either Walmart or Exxon Mobil has occupied the top spot. With revenue of $496 billion in its most recent fiscal year, the global retailing giant is the world’s largest company by revenue. Because these are the country’s largest companies, any meaningful deterioration in size — rather than simply in response to cyclical economic and sectoral forces — usually takes years, if not decades to manifest. Gradual changes in size over the longer term among Fortune 500 companies reflect larger trends in the U.S. economy. For example, the decline of automobile company GM and the rise of retailer Walmart over the past 50 years reflect the decline of American manufacturing and the rise of the service sector over that time…”