A battlefield of 3,250 years ago in Germany is yielding remains of wounded warriors, wooden clubs, spear points, flint and bronze arrowheads and bronze knives and swords. The gruesome scene, frozen in time by peat, is unlike anything else from the Bronze Age in Northern Europe, where, researchers thought, large-scale warfare didn’t begin until later. Analysis of the remains of the 130 men, most between ages 20 and 30, found so far shows some may have been from hundreds of kilometers away—Poland, Holland, Scandinavia and Southern Europe. The hand-to-hand combat of the battle, which may have involved thousands of people...