William of Orange arrived with his forces in Ireland in June of 1690. They made their way to the spot on the Boyne river where the Jacobites had made their strategic defensive base. The famed battle took place one the 12th of July in our modern calendar and was fought for control of a ford in the river near the town of Drogheda. As William sent a portion of his men to cross the river at a different point, James became panicked that he was going to be surrounded. He sent half of his troops away to deal with the incoming Williamite men, a decision which would prove foolish as both sides were held back by a deep ravine and so were unable to reach one another.
Back at the main site of the battle, the Williamites were able to cross the ford by sheer force and firepower. A counter attack from the Jacobite cavalry saw the Williamites driven back somewhat but they continued to push through with the aid of their own mounted soldiers. This was the main portion of the battle and it saw men being severely injured on both sides. The losses were great, but after much arduous fighting, the Williamites prevailed and were able to take hold of Donore where they could rest before pursuing the Jacobite retreat. The pursuit failed and the Williamites returned to tend to their wounded.
Though the battle was significant, the loss of life was surprisingly low. Approximately 2,000 men were killed of the 50,000 who fought that day. Compared with the 7,000 dead of the Battle of Aughrim a year later, this is a rather small number of casualties. The Williamites would continue to pursue their cause in Ireland, defeating the Jacobites again at Aughrim and finally bringin the war to an end with the signing of the treaty of Limerick after a lengthy siege. This treaty resulted in the Jacobite army and their families either swearing loyalty to William, or else leaving Ireland for France in what would be known as the Flight of the Wild Geese.