Strewn with mines and bordered with barbed wire, the demilitarized zone between North and South Korea extends in a narrow band about 150 miles long and two and a half miles wide. No permanent structures or settlements exist in the DMZ, and over the past 50 years, only occasional soldiers, observers, and the 225 residents of Daeseong-dong, a little village on the southern border, have been allowed in. Because of this imposed isolation, the politically tense zone is an inadvertent haven for wildlife.

Regions like this, which were once part of a war zone, can ironically sometimes become a no-man's-land where animals and plants flourish free of human interference. Even in countries with no recent conflicts, conservationists are exploring how border zones, which tend to be unpopulated, could be used to preserve wildlife.

In the case of the Korean DMZ, population growth on both sides, as well as land conversion and development, has forced wildlife—including rare species—into the zone. Although the terrain is mostly mountainous, the zone includes the Han River delta and extensive grasslands. White-naped and red-crowned cranes use it seasonally; black-faced spoonbills, swan geese, Angora goats, Amur leopards, and the Asiatic black bear thrive year-round.

Remarkably, a few rare Amur tigers (also known as Siberian tigers) may also hang on in the DMZ. While some still exist in ­eastern Siberia and the Kamchatka peninsula, only about 10 live in South Korea, and there are no data from North Korea. But farmers who live next to the DMZ have seen pug marks, the scratches large cats make to mark their territories, and locals have also reported animals apparently mauled by a large predator. To find tigers in the DMZ would be great news for the future of the species—and not just because of the boost in numbers. In Korea the tiger has such symbolic importance that its presence in the DMZ might prove a compelling counterargument to the myriad plans for joint development in the zone, which include an international trade center, hotels, tourism programs, and housing.

The 1982 Falklands War between Argentina and the United Kingdom over ownership of a group of small islands in the South Atlantic Ocean also had an unexpected ecological benefit. In that brief span of time, Argentine forces created 150 minefields, mostly around the coastal town of Stanley, the capital. Home to about 1,500 of the islands' 2,900 citizens, Stanley also attracts about 40,000 tourists each summer to observe the region's distinctive bird and marine life. After the war, both sides worked together to remove the mines, but an estimated 15,000 to 25,000 remain scattered across 117 minefields. For four species of penguin that use the area for breeding—gentoos, southern rockhoppers, Magellanics, and kings—the mines are a boon. Because the penguins are apparently too light for their footsteps to set off the explosive devices, the birds now congregate in fenced minefields that are off-limits to people and livestock. Their new haven, however, doesn't protect these penguins from the impact of commercial fishing, which harvests the squid and fish they depend upon. As a result of the diminished food supply, local penguins have become less successful at raising chicks. Despite the minefields, the number of penguins at various sites in the Falklands has declined by roughly 84 percent since the war ended.

The paradoxical impact of battle is unmistakable in the regions involved in the Vietnam War. Between 1961 and 1971, U.S. forces dropped an estimated 100,000 tons of herbicides and defoliants on Vietnam, Laos, and Cambodia. In many places, tropical forests were reduced to single-species grasslands. Such devastating simplification of habitat led to marked declines in species, including ­elephants, Javanese rhinos, deer, and wild cats.