Rajasingha's father had long courted the Dutch as a potential ally against the Portuguese. A treaty had been signed between Kandy and Dutch envoy Marcelis Boschouwer but had not amounted to much. Soon after Rajasingha's accession however the Dutch, now firmly established in
Batavia, put Portuguese
Goa under a blockade. On 28 March 1638, Rajasingha led his army to victory against the Portuguese forces at
Gannoruwa. Soon after this, Rajasingha sent a request for aid to the admiral Adam Westerwolt and by 23 May 1638 had signed an extensive military and trade treaty with them. The Dutch seized
Batticaloa on 18 May 1639 and a joint Kandyan–Dutch campaign began to make inroads into Portugal's lowland territories. The alliance was however deeply unpopular with the inhabitants of Kandy. Tensions soon arose between the two parties. Batticaloa was the traditional port of the Kandyan kingdom (
Trincomalee had long been lost, first to the
Jaffna kingdom and then to the Portuguese), and Rajasingha was eager to acquire it as soon as possible. The Dutch, however, demurred, demanding full payment for their assistance in displacing the Portuguese. Despite a rising suspicion that the Dutch were not in Sri Lanka to expel the Portuguese, so much as to replace them, the alliance was one that was too valuable for Rajasingha to simply cancel, and joint Dutch–Kandyan efforts resulted in the seizure of
Galle on 13 March 1640 and the restriction of Portuguese power to the west coast of Sri Lanka by 1641. The slow end of the
Eighty Years' War however soon resulted in a truce being called between Dutch and Portuguese forces in Sri Lanka (the crowns of Spain and Portugal were united between 1580 and 1640) sometime between 1641 and 1645. Rajasinga, and many of his advisers, furiously concluded that the Dutch intended to carve Sri Lanka up with the Portuguese, to the detriment of native power. The alliance of 1638 came to an abrupt end and Kandy launched into what was to be a hundred years of intermittent warfare with the Dutch. The period between 1645 and 1649 saw the Kandyan adopting a
scorched earth policy in eastern Sri Lanka. Capturing and annexing Dutch held territory was out of the question for the Kandyans who could muster neither the firepower nor the manpower for an occupation. Nevertheless, Rajasingha's policy of intentionally burning crops and depopulation villages drove the Dutch to the negotiating table and in 1649 and the Kandyan-Dutch alliance was resurrected, albeit on slightly different terms. ==Later reign: stalemate==