A 21st-century land rush is on. Driven by fear and lured by promises of high profits, foreign investors are scooping up vast tracts of farmland in some of the world’s hungriest countries to grow crops for export.

As the climate changes and populations shift and grow, billions of people around the globe face shortages of land and water, rising food prices and increasing hunger. Alarm over a future without affordable food and water is sparking unrest in a world already tinder-dried by repression and recession, corruption and mismanagement, boundary disputes and ancient feuds, ethnic tension and religious fundamentalism.

World leaders feel the heat. Calling food security concerns “extremely significant,” a 2009 U.N. report noted, “The acquisition of land internationally is one possible strategic choice to address the challenge.”

Fortunately for nervous rulers, the strategy of growing food abroad as shelter against the fires of revolution dovetails nicely with the goals of private and public capital. Governments drawing on sovereign wealth funds, and rich investors accessing state subsidies, have negotiated deals to acquire tens of millions of acres of farmland in Africa, South America and South Asia. When they export the food to their home countries, the valuable water used to grow the crops will ride along as a free bonus.

The largest investors in foreign croplands hail from China, India and South Korea, along with Saudi Arabia and other oil-rich Gulf states. What these countries have in common is that all were shaken financially or politically by the 2007-08 food crisis. And all lack sufficient land or water to ensure that they can feed their populations in the coming years–especially if, as the Food and Agriculture Organization (FAO) warns, climate change continues to “exacerbate land degradation and water scarcity in many places, and to increase the frequency of extreme weather events affecting harvests.”...