Before Richelieu's ascent to power, most of Europe had become enmeshed in the Thirty Years' War (1618–1648). France was not openly at war with the Habsburgs, who ruled Spain and the Holy Roman Empire, so subsidies and aid were provided secretly to their adversaries. He considered the Dutch Republic as one of France's most important allies, for it bordered directly with the Spanish Netherlands and was right in the middle of the Eighty Years' War with Spain at that time. Luckily for him, Richelieu was a "bon français", just like the king, who had already decided to subsidize the Dutch to fight against the Spanish via the Treaty of Compiègne in June 1624, prior to Richelieu's appointment to First Minister in August. That same year, a military expedition, secretly financed by France and commanded by Marquis de Coeuvres, started an action with the intention of liberating the Valtelline from Spanish occupation. In 1625, Richelieu also sent money to Ernst von Mansfeld, a famous mercenary general operating in Germany in English service. However, in May 1626, when war costs had almost ruined France, king and cardinal made peace with Spain via the Treaty of Monçon. This peace quickly broke down after tensions due to the War of the Mantuan Succession.