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America Retold: 250 years of the United States and the world. Read more from the series.

In July 1943, while Americans were invading Sicily and island-hopping across the Southwest Pacific, residents of Los Angeles thought they were targets of a Japanese chemical warfare attack. The air smelled like bleach and corroded rubber tires. Pilots could not see through brown clouds to land their planes safely.

Los Angelenos were indeed victims of a surprise chemical attack, but it was not Japanese. Rather, it was photochemical smog, an attack of their own making. The wartime boom had brought more people, cars, and industry to greater Los Angeles. Tailpipe and smokestack emissions combined with sunshine to brew up thick smog that obscured the sky, gnawed tires, and irritated raspy throats and itchy eyes.

In July 1943, while Americans were invading Sicily and island-hopping across the Southwest Pacific, residents of Los Angeles thought they were targets of a Japanese chemical warfare attack. The air smelled like bleach and corroded rubber tires. Pilots could not see through brown clouds to land their planes safely.

Los Angelenos were indeed victims of a surprise chemical attack, but it was not Japanese. Rather, it was photochemical smog, an attack of their own making. The wartime boom had brought more people, cars, and industry to greater Los Angeles. Tailpipe and smokestack emissions combined with sunshine to brew up thick smog that obscured the sky, gnawed tires, and irritated raspy throats and itchy eyes.

The United States has had an outsized impact on world affairs at least since World War II, if not earlier. It has also had an outsized impact on the planet itself, its ecosystems, biota, and climate. This is partly because the United States was, already by the 19th century, a big country that mobilized a lot of resources, from beaver fur and bison leather to oil and steel. And it is partly because the United States pioneered some innovative models—including car culture, industrial farming, and national parks—that had profound ecological consequences.

For better or worse, this form of U.S. primacy is unlikely to last. China appears to be destined to wield greater influence than the United States over the condition of the Earth—if it doesn’t already.

A watercolor print depicts an early American whaling expedition, with a large whale destroying a whaling ship, circa 1875. GraphicaArtis/Getty Images

From the dawn of the republic, Americans exercised powerful and direct effects on wildlife at sea and on land. By killing animals such as beaver, whales, and bison, they triggered ecological impacts that transformed ecosystems in North America and beyond.

Fur trappers sprang into action well before the foundation of the United States, responding to a fashion craze for beaver hats and coats. At the time of the American Revolution, North America’s beaver population stood at roughly 150 million. That fell fast, as trapping peaked between 1790-1840, by which time beavers were running low. By 1900, only about 100,000 remained, and some 4 million tons of beaver biomass had vanished.

Since beavers are energetic ecosystem engineers, building dams and creating ponds, the near elimination of beavers altered the face of North America. Most beaver ponds drained away. Streams ran faster. Rivers eroded their banks more quickly and dumped more sediment at their mouths. Beaver ponds emit methane to the atmosphere, so the disappearance of maybe 30 million ponds moderated methane emissions a little bit, postponing the onset of global warming very slightly.

Between 1780 and 1880, Yankee whalers operating out of Nantucket and New Bedford played the leading role in cutting the oceans’ sperm whale population by one-third. Sperm whale oil proved crucial to industrialization. It provided illumination and, more importantly, a superb all-weather machine lubricant used in guns; locomotives; watches; cotton-mill spindles; and, until the 1970s, cars’ automatic transmissions.

By 1880, the oceans had lost 10 million tons worth of sperm whale biomass. As a result, oceanic food webs thinned slightly, because sperm whales play a major role in fertilizing surface waters. They hunt in the depths for their........

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