The next year, thanks to the fact that the Cardinal-Infante shifted the focus of his campaign to the French border in that year, Frederick Henry managed to recapture Breda with a relatively small force, at the successful fourth Siege of Breda, (21 July–11 October 1637). This operation, which engaged his forces for a full season, was to be his last success for a long time, as the peace party in the Republic, over his objections, managed to cut war expenditure and shrink the size of the Dutch army. These economies were pushed through despite the fact that the economic situation in the Republic had improved appreciably in the 1630s, following the economic slump of the 1620s caused by the Spanish embargoes. The Spanish river blockade had ended in 1629. The end of the Polish–Swedish War in 1629 ended the disruption of Dutch Baltic trade. The outbreak of the Franco-Spanish War (1635) closed the alternate trade route through France for Flemish exports, forcing the South to pay the heavy Dutch wartime tariffs. Increased German demand for foodstuffs and military supplies as a consequence of military developments in that country, contributed to the economic boom in the Republic, as did successes of the VOC in the Indies and the WIC in the Americas (where the WIC had gained a foothold in Portuguese Brazil after its 1630 invasion, and now conducted a thriving sugar trade). The boom generated much income and savings, but there were few investment possibilities in trade, due to the persisting Spanish trade embargoes. As a consequence, the Republic experienced a number of speculative bubbles in housing, land (the lakes in North Holland were drained during this period), and, notoriously, tulips. Despite this economic upswing, which translated into increased fiscal revenues, the Dutch regents showed little enthusiasm for maintaining the high level of military expenditures of the middle 1630s. The échec of the Battle of Kallo of June 1638 did little to get more support for Frederick Henry's campaigns in the next few years. These proved unsuccessful; his colleague-in-arms Hendrik Casimir, the Frisian stadtholder died in battle during the unsuccessful siege of Hulst in 1640.