The sign describes the technique of how they made the previously-too-acidic rivers (from an excess of pine trees and tannic acid in the surroundings) usable again, involving small dams, deposits of crushed limestone, and natural water agitation to counteract the tannic acid and bring the river...
Soviets invaded Afghanistan.The Soviet Union, through the invasion of Afghanistan in support of the Afghan communist government, in effect launched a series of chain reactions that had the most profound consequences today. First and foremost, the Soviets hastened its own collapse by expending an extr...