By extracting sediment cores from Lake Malawi, one of the largest and deepest lakes on Earth, scientists determined in 2007 that sub-Saharan Africa experienced a series of mega-droughts from 135,000 to 90,000 years ago. Rainfall was so scarce, in fact, that the lake’s water level dropped some 2,000 feet, and lush forests turned into arid scrubland.

The return of wetter conditions, coinciding as they did with an expanded Nile corridor, may have then provided humans with an ideal window for leaving Africa and colonizing the world, scientists say.

Nile Delta sediments show that the amount of wetland pollen decreased about 4,200 years ago and that the amount of charcoal (a sign of fire) increased, leading scientists to believe that a drought must have occurred. They furthermore speculate that this lack of rain contributed to the demise of Egypt’s Old Kingdom, best known for constructing the massive pyramids of Giza. Other civilizations to decline around that time, possibly as a result of the same drought, include the Harappa of present-day northwest India and Pakistan, the Subir of present-day Syria and the Minoan of Crete.

During their so-called Classic Period from approximately A.D. 250 to the 9th century, the Maya built dozens of monumental stone cities while at the same time making impressive strides in mathematics, agriculture, astronomy, writing and art. Then it all fell apart, a collapse in which drought almost certainly played a role.

Numerous studies illustrate that the Maya endured centuries of low rainfall from roughly the 600s to the 1100s and that the main episodes of city abandonment from 760 to 910 appear to coincide with particularly dry years. Scientists contend that the drought’s effects were then exacerbated by warfare, political instability and land degradation.

With the Great Depression already making life difficult, a drought struck the Great Plains in 1931 and essentially lasted for the rest of the decade. Combined with short-sighted agricultural practices, it induced huge clouds of dust that turned the skies dark, lodged in residents’ lungs, and precipitated a mass migration to greener pastures. The apex came in 1934, which NASA researchers recently called the worst drought year of the last millennium in North America. Not far behind was 1936, when, amid the dust storms, a devastating summer heat wave killed upwards of 5,000 Americans and 1,100 Canadians.

Amid the chaos of World War II, one of China’s worst droughts in decades hit Henan Province, part of the country’s traditional breadbasket region. Winds, hailstorms and locusts compounded the situation, and in 1942 grain harvests in the portion of the province not occupied by Japan dropped to roughly a quarter of their normal output. To make matters worse, much of that food went to soldiers. Forced to eat roots and bark, as many as 3 million Chinese died of starvation by the end of the following year and millions more became refugees.

Following a 1950s dry spell, no widespread drought hit the United States until the late 1980s, when prime corn and soybean country in the Northern Great Plains began suffering from low rainfall. Spreading both east and west, the drought was then blamed for the many heat waves and forest fires that broke out in the summer of 1988. In and around Yellowstone National Park, for example, a blaze torched about 1.2 million acres, closing the entire park for the first time. Researchers later estimated the cost of this three-year drought at $39 billion, marking it as the most expensive U.S. natural disaster up to that point.

Experts increasingly believe that Syria’s worst drought on record last decade may have sparked the country’s civil war, an ongoing, multi-sided affair that has claimed the lives of more than 200,000 people.

During the drought, roughly 1.5 million Syrians from farming villages fled to cities as their livestock died and their fields turned to desert. Rather than sympathy, however, they were met with alleged indifference from the government of President Bashar al-Assad, which, among other things, cut their food and energy subsidies. With sectarian tensions adding to their discontent, a number of these newly unemployed farmers joined peaceful protests against Assad in 2011 that quickly boiled over into violent conflict.