The Great Leap Forward was a push by Mao Zedong to change China from a predominantly agrarian (farming) society to a modern, industrial society - in just five years.
Between 1958 and 1960, millions of Chinese citizens were moved onto communes. Some were sent to farming cooperatives, while others worked in small manufacturing. All work was shared on the communes; from childcare to cooking, daily tasks were collectivized.
Mao hoped to increase China's agricultural output. He relied, however, on nonsensical Soviet farming ideas, such as planting crops very close together so that they could support one another, and plowing up to six feet deep to encourage root growth.
Mao also wanted to free China from the need to import steel and machinery. He encouraged people to set up back-yard steel furnaces, where citizens could turn scrap metal (and their own pots, pans and farm implements) into usable steel.
The results were predictably bad. Backyard smelters run by peasants with no metallurgy training produced such low-quality iron that it was worthless.
Over just a few years, the Great Leap Forward caused massive environmental damage in China. The backyard steel production plan resulted in entire forests being burned to fuel the smelters, which left the land open to erosion. Dense cropping and deep ploughing stripped the farmland of nutrients and left the agricultural soil vulnerable to erosion, as well.
When autumn of 1958 came, many areas had a bumper crop, since the soil was not yet exhausted. However, so many farmers had been sent into steel production work that there weren't enough hands to harvest the crops.
Anxious commune leaders vastly exaggerated their harvests, hoping to curry favor with the Communist leadership. As a result, Party officials carried off most of the food to serve as the cities' share of the harvest, leaving the farmers with nothing to eat. People in the countryside began to starve.
The next year, the Yellow River flooded, killing 2 million people either by drowning or by starvation after crop failures. In 1960, a wide-spread drought added to the nation's misery.
In the end, through a combination of disastrous economic policy and adverse weather conditions, an estimated 20 to 48 million people died in China. Most starved to death in the countryside. The official death toll from the Great Leap Forward is "only" 14 million, but most scholars agree that this is a substantial underestimate.
The Great Leap Forward was supposed to be a 5-year plan, but it was called off after just three tragic years. The period between 1958 and 1960 is known as the "Three Bitter Years" in China.