viruses such as the West Nile virus continued to spread. Malaria and other diseases affected large populations. Millions were infected with HIV, the virus which causes AIDS. The virus was becoming an epidemic in southern Africa. Based on research done by climate scientists, the majority of the scientific community consider that in the long term environmental problems pose a serious threat. One argument is that of global warming occurring due to human-caused emission of greenhouse gases, particularly carbon dioxide produced by the burning of fossil fuels. This prompted many nations to negotiate and sign the Kyoto treaty, which set mandatory limits on carbon dioxide emissions. World population increased from about 1.6 billion people in 1901 to 6.1 billion at the century's end. Wars and politics The number of people killed during the century by government actions was in the hundreds of millions. This includes deaths caused by wars, genocide, politicide and mass murders. The deaths from acts of war during the two world wars alone have been estimated at between 50 and 80 million. Political scientist Rudolph Rummel estimated 262,000,000 deaths caused by democide, which excludes those killed in war battles, civilians unintentionally killed in war and killings of rioting mobs. According to Charles Tilly, "Altogether, about 100 million people died as a direct result of action by organized military units backed by one government or another over the course of the century. Most likely a comparable number of civilians died of war-induced disease and other indirect effects." It is estimated that approximately 70 million Europeans died through war, violence and famine between 1914 and 1945. The Armenian, Syriac and Greek genocide were the systematic destruction, mass murder and expulsion of the Armenians, Assyrians and Greeks in the Ottoman Empire during World War I, spearheaded by the ruling Committee of Union and Progress (CUP). Rising nationalism and increasing national awareness were among the many causes of World War I (1914–1918), the first of two wars to involve many major world powers including Germany, France, Italy, Japan, Russia/USSR, the British Empire and the United States. World War I led to the creation of many new countries, especially in Eastern Europe. At the time, it was said by many to be the "war to end all wars". After gaining political rights in the United States and much of Europe in the first part of the century, and with the advent of new