until 1868, Bonaire remained a government plantation. In 1825, there were about 300 government-owned slaves on the island. Gradually many of the slaves were freed and became freemen with an obligation to render some services to the government. The remaining slaves were freed on 30 September 1862 under the Emancipation Regulation. A total of 607 government slaves and 151 private slaves were freed at that time. World War II During the German occupation of the Netherlands during World War II, Bonaire was a protectorate of Britain and the United States. The American army built the Flamingo Airport as an air force base. After Germany invaded the Netherlands on May 10, 1940, authorities declared Martial law, and many German and Austrian citizens, as well as Dutch thought to be German sympathizers, were interned in a camp on Bonaire. Some of these remained in this camp for the war's duration, and others were transferred to new camps that were built on the mainland in the first year of the war. In 1944, Princess Juliana and Eleanor Roosevelt visited the troops on Bonaire. Bonairean sailors made an above-average contribution during World War II. German U-boats tried to eliminate shipping around the Aruba and Curaçao refineries and thus eliminate the island's considerable fuel production for the Allies. Bonairean crewed ships also took part in these battles. Among the many, missing after the war, were the 34 Bonaireans who died on these ships (more than on the other islands of the then Dutch West Indies). During hostilities, the site where the Divi Flamingo Beach Resort & Casino now stands served as an internment camp for Germans and Austrians living in the Antilles, mainly because they were distrusted. There were fears they could have sabotaged the giant oil refineries on Aruba and Curaçao that were supplying paraffin to the Allied air fleet. The camp was in operation from 1940 to 1947. In total, 461 people were interned during this period without trial, most of them completely innocent. Among them were Medardo de Marchena and also the photographer Fred Fischer, then still an Austrian citizen. Many German internees had just fled Nazi violence. But there were also German prisoners of war, some of whom remained after the war. In September 1943, the father of George Maduro, after whom Madurodam is named, asked Queen Wilhelmina to exchange his son for the German internees on Bonaire. The government did