they would then use to purchase Mainau. Wilhelm was instrumental in the preparations for the Franco-Dutch War. He went between France and numerous rulers in the Empire to try and build an unbeatable alliance for the attack on the Dutch. In 1670 he secured French support for the army of Cologne, guaranteeing the interests of Maximilian in the treaty. He then went to convince Frederick William, Elector of Brandenburg, to join the offensive alliance, though he was ultimately unsuccessful. By July 1671, Wilhelm convinced the Bishop of Münster to join the French alliance. Downfall and rescue During the negotiations in 1666 with Münster in the Second Anglo-Dutch War, Wilhelm found himself opposed by the Elector of Brandenburg. In 1670, while attempting to get Brandenburg to join the French alliance in the Franco-Dutch War, Wilhelm also asked the elector about his opinion of a successor for Leopold I, who was sick at the time. Wilhelm suggested again Louis XIV as the next Emperor, but Brandenburg preferred the Duke of Neuburg. When Wilhelm went to leave, he was delayed by the disappearance of some of his baggage, which included his money and diplomatic papers. The bags turned up the next day without the money, so Wilhelm considered it simple theft. He did not notice that his papers had been searched, and that the document detailing his discussions and plans for the Emperor's replacement was missing. This document would show up again as evidence of his treason against the Emperor at his trial. In 1671, the Elector of Brandenburg spoke many times to Leopold against the influence that Wilhelm was wielding on behalf of France, and the Emperor became more strongly opposed to Wilhelm's work. In 1672 the Emperor joined the Franco-Dutch War as an ally of the Dutch, finding himself opposed by several bishops in the northwest part of the Empire. The Fürstenberg brothers being regarded by the Imperialists as the main cause of this disaster, Wilhelm was arrested for treason on 14 February 1674 by imperial cavalry after chasing his carriage through Cologne. At the time of his arrest he was making ninety thousand livres a year from France. He was hurried off to Vienna and was tried for his life. He was saved by the intervention of the papal nuncio at Cologne, but was kept in prison until the signature of the Treaty of Nijmwegen in 1679. As a reward