The final days of the Dutch Republic, which had governed the Netherlands since the late 16th century, were quite eventful. Due to the disastrous Fourth Anglo-Dutch War, the Patriot party revolted against the authoritarian regime of stadtholder William V but were quickly struck down through the intervention of William's brother-in-law Frederick William II in September 1787. Most Patriots went into exile in France, while Holland's own "Ancien Régime" strengthened its grip on Dutch government chiefly through the Orangist Grand Pensionary Laurens Pieter van de Spiegel. This "de facto" status of Anglo-Prussian protectorate was internationally formalized in 1788 by the Act of Guarantee (for which Great Britain and Prussia acted as guarantors) and the Triple Alliance between the Dutch Republic, Prussia and Great Britain.