Fijians, approximately one-third of the population, in 1875, and in the early 19th century devastated the Great Andamanese population. The Ainu population decreased drastically in the 19th century, due in large part to infectious diseases brought by Japanese settlers pouring into Hokkaido. Researchers concluded that syphilis was carried from the New World to Europe after Columbus's voyages. The findings suggested Europeans could have carried the nonvenereal tropical bacteria home, where the organisms may have mutated into a more deadly form in the different conditions of Europe. The disease was more frequently fatal than it is today. Syphilis was a major killer in Europe during the Renaissance. Between 1602 and 1796, the Dutch East India Company sent almost a million Europeans to work in Asia. Ultimately, fewer than a third made their way back to Europe. The majority died of diseases. Disease killed more British soldiers in India and South Africa than war. As early as 1803, the Spanish Crown organized a mission (the Balmis expedition) to transport the smallpox vaccine to the Spanish colonies and establish mass vaccination programs there. By 1832, the federal government of the United States established a smallpox vaccination program for Native Americans. From the beginning of the 20th century onwards, the elimination or control of disease in tropical countries became a driving force for all colonial powers. The sleeping sickness epidemic in Africa was arrested due to mobile teams systematically screening millions of people at risk. In the 20th century, the world saw the biggest increase in its population in human history due to a drop in the mortality rate in many countries as a result of medical advances. The world population has grown from 1.6 billion in 1900 to an estimated 6.8 billion in 2011. Cholera Since it became widespread in the 19th century, cholera has killed tens of millions of people. 1817–1824 cholera pandemic. Previously restricted to the Indian subcontinent, the pandemic began in Bengal, then spread across India by 1820. 10,000 British troops and thousands of Indians died during this pandemic. It extended as far as China, Indonesia (where more than 100,000 people succumbed on the island of Java alone) and the Caspian Sea before receding. Deaths in the Indian subcontinent between 1817 and 1860 are estimated to have exceeded 15 million. Another 23 million died between 1865 and 1917. Russian deaths during a similar period exceeded 2million. 1826–1837 cholera pandemic. Reached