An excerpt from the Smithsonian article...

In his book Enriching the Earth: Fritz Haber, Carl Bosch and the Transformation of World Food Production, Vaclav Smil pointed out that "there is no way to grow crops and human bodies without nitrogen." Before Haber's invention, the sheer amount of life earth could support—the size of crops and therefore the number of human bodies—was limited by the amount of nitrogen that bacteria and lightning could fix. By 1900, European scientists had recognized that unless a way was found to augment this naturally occurring nitrogen, the growth of the human population would soon grind to a very painful halt. The same recognition by Chinese scientists a few decades later is probably what compelled China's opening to the West: after Nixon's 1972 trip, the first major order the Chinese government placed was for 13 massive fertilizer factories. Without them, China would have starved.This is why it may not be hyperbole to claim, as Smil does, that the Haber-Bosch process for fixing nitrogen (Bosch gets the credit for commercializing Haber's idea) is the most important invention of the 20th century. He estimates that two of every five humans on earth today would not be alive if not for Fritz Haber's invention. We can easily imagine a world without computers or electricity, Smil points out, but without synthetic fertilizer billions of people would never have been born. Though, as these numbers suggest, humans may have struck a Faustian bargain with nature when Fritz Haber gave us the power to fix nitrogen.Fritz Haber? No, I'd never heard of him either, even though he was awarded the Nobel Prize in 1918 for "improving the standards of agriculture and the well-being of mankind." But the reason for his obscurity has less to do with the importance of his work than an ugly twist of his biography, which recalls the dubious links between modern warfare and industrial agriculture: during World War I, Haber threw himself into the German war effort, and his chemistry kept alive Germany's hopes for victory, by allowing it to make bombs from synthetic nitrate. Later, Haber put his genius for chemistry to work developing poison gases—ammonia, then chlorine. (He subsequently developed Zyklon B, the gas used in Hitler's concentration camps.) His wife, a chemist sickened by her husband's contribution to the war effort, used his army pistol to kill herself; Haber died, broken and in flight from Nazi Germany, in a Basel hotel room in 1934.