For not fighting over

Wolf and his colleagues combed through thousands of newspaper clippings and historical accounts of anything having to do with water at international borders. He ranked every event on a scale of -7 to +7, with numbers below zero indicating worsening degrees of conflict, and numbers above zero pointing to increasing degrees of collaboration. “It turns out two-thirds of the time we do anything over water, we cooperate,” Wolf says. “There was a whole rich history that isn’t covered anywhere.”

In a warming world, the fight for water can push nations apart—or bring them together