Shortly after George's accession in Hanover, the War of the Spanish Succession broke out. At issue was the right of Philip, the grandson of King Louis XIV of France, to succeed to the Spanish throne under the terms of King Charles II of Spain's will. The Holy Roman Empire, the United Dutch Provinces, England, Hanover and many other German states opposed Philip's right to succeed because they feared that the French House of Bourbon would become too powerful if it also controlled Spain. As part of the war effort, George invaded his neighbouring state, Brunswick-Wolfenbüttel, which was pro-French, writing out some of the battle orders himself. The invasion succeeded with few lives lost. As a reward, the prior Hanoverian annexation of the Duchy of Saxe-Lauenburg by George's uncle was recognised by the British and Dutch.Hatton, pp. 86–89.
