A flamethrower is a device designed to project a stream of ignited flammable liquid, typically for military or controlled burning purposes.  They originated in ancient times, with early versions used by the Byzantine Empire in the 7th century AD via “Greek fire,” but modern designs emerged during World War I, pioneered by Germany.  In warfare, flamethrowers were effective for clearing trenches, bunkers, and fortified positions by shooting flames that could arc around corners, deplete oxygen in enclosed spaces, and instill psychological terror in enemies.  They saw extensive use in World War II, particularly by U.S. forces in the Pacific theater against Japanese defenses, and later in conflicts like Vietnam.  Militaries have largely phased them out due to international protocols (like the 1980 UN Convention on Certain Conventional Weapons, which restricts but doesn’t fully ban them) and the rise of more precise incendiary weapons.