Thirty Years' War

Before Richelieu's ascent to power, most of Europe had become involved in the Thirty Years' War. In 1629, the Habsburg Holy Roman Emperor humbled many of his Protestant opponents in Germany, thereby greatly increasing his power. Cardinal Richelieu, alarmed by the Emperor Ferdinand II's influence, incited Sweden to attack. He also agreed to aid King Gustavus II Adolphus of Sweden with financial subsidies. France was not openly at war with the Empire, so aid was given secretly. In the meantime, France and Spain continued to remain hostile over the latter kingdom's ambitions in northern Italy. At that time Northern Italy was a major strategic asset in Europe's balance of powers, being a terrestrial link between the Habsburg's two branches in Germany and Spain. Had the imperial armies dominated this region, France's very existence would have been endangered, being circled by Habsburg territories. Spain was then aspiring for becoming a "universal monarchy", with support from the Pope. When, in 1630, French ambassadors in Regensburg agreed to make peace with Habsburg Spain, Richelieu refused to uphold them. The agreement would have prohibited French interference in the hostilities in Germany. Thus, Richelieu advised Louis XIII to refuse to ratify the treaty.

Because he openly aligned France with Protestant powers, Richelieu was denounced by many as a traitor to the Roman Catholic Church. Military hostilities, at first, were disastrous for the French, with many victories going to Spain and the Empire. Neither side, however, could obtain a decisive advantage, and the conflict lingered on until after Richelieu's death.

Military expenses put a considerable strain on the King's revenues. In response, Cardinal Richelieu raised the gabelle (a tax on salt) and the taille (a tax on land). The taille was enforced to provide funds to raise armies and wage war. The clergy, nobility, and high bourgeoisie were either exempt or could easily avoid payment, so the burden fell on the poorest segment of the nation. To collect taxes more efficiently, and to keep corruption to a minimum, Richelieu bypassed local tax officials, replacing them with intendants—officials in the direct service of the Crown. Richelieu's financial scheme, however, caused unrest amongst the peasants; there were several uprisings between 1636 and 1639. Cardinal Richelieu crushed the revolts violently, and dealt with the rebels harshly.