TRES MARIAS RANCH, Brazil - On May 12, Gabriel Maciel and more than 1,000 other landless farmers knocked down the barbed-wire fences surrounding the Tres Marias ranch in southern Brazil, evicted its owner and claimed the land for themselves. "This is our land now and no one will take it away from us," he says a few weeks later, as his wife, Remy, cooks rice and beans over a fire by their hut of bamboo stakes and black plastic sheeting. Less than 50 miles away, gunmen in masks patrol the perimeter of another ranch whose owner vows to fight back...