The Germans attacked The Netherlands on May 10, 1940 to provide access to France to bypass the Maginot Line and entice the Allies to cross the Dutch border to attack their spearhead in Belgium. German paratroopers sustained heavy casualties in their drops on Dutch airfields, and there was heroic but doomed Dutch resistance. Within five days they had surrendered. After the surrender, the same day, a German bombing mission could not be recalled in time and killed 40,000 in Rotterdam.
Dutch citizens endured a brutal occupation. The Gestapo was grimly successful in routing the Jewish population of Holland and sending them to death in the concentration camps.
Queen Wilhelmina of the Netherlands evacuated to London and formed a government-in-exile. The Dutch colonies in the Pacific continued to provide resources for the Allies until the Japanese attacked in December 1941. In March 1942 the Dutch Admiral Karel Doorman led the ABDA naval units in a losing battle against superior Japanese forces. He was killed when his cruiser, the DeReuyter, was sunk.
Dutch submarines continued to harass the Japanese throughout the war in conjunction with the American submarine blockade of Japan. Other Dutch warships served in the Atlantic.
Montgomery invaded Holland and Belgium as part of Operation Market-Garden in September 1944, but he failed to complete all of his objectives. The Winter of 1944 for very hard on the Dutch. They were left to starve by a German Army that could barely supply their own troops. Thousands died of starvation. Canadian, American and British troops held a fairly static front in Holland until the end of European hostilities in May 1945.
In the Pacific, the Dutch contribution to victory over Japan was mitigated by their dependence on Britain and America for arms and supplies. But they formed an important part of the Allied Navies in the Pacific during the darkest years.