The Brush Wars were a series of conflicts that took place in the mid-20th century on Earth, on the continent of Asia. They were characterized by two superpowers aiding and assisting lesser nations in their conflict with each other. The Brush Wars went on "bloody year after bloody year," according to one 23rd century observer. The Brush Wars were unpopular in some countries on Earth, with riots breaking out, in particular among young student populations. One such riot was held at Santa Cruz in 1967, requiring police forces to break up the riot with tear gas. (VOY: "Future's End")