The 20th century began on 1 January 1901 (MCMI), and ended on 31 December 2000 (MM). It was the last century of the 2nd millennium, and was marked by new models of scientific understanding, unprecedented scopes of warfare, new modes of communication that would operate at nearly instant speeds and new forms of art and entertainment.
The 20th century was dominated by significant geopolitical events that reshaped the political and social structure of the globe: World War I, the Spanish flu pandemic, World War II and the Cold War. Unprecedented advances in science and technology defined the modern era, including the advent of nuclear weapons and nuclear power, space exploration, the shift from analogue to digital computing and the continuing advancement of transportation, including powered flight and the automobile. The Earth's sixth mass extinction event, the Holocene extinction, continued, and human conservation efforts increased.
Major themes of the century include decolonization, nationalism, globalization and new forms of intergovernmental organizations. Cultural homogenization began through developments in emerging transportation and information and communications technology. Poverty was reduced and the century saw rising standards of living, world population growth, awareness of environmental degradation and ecological extinction. Automobiles, airplanes and home appliances became common, and video and audio recording saw mass adoption. Great advances in electricity generation and telecommunications allowed for near-instantaneous worldwide communication, ultimately leading to the Internet. Meanwhile, advances in medical technology resulted in the near-eradication and eradication of many infectious diseases, as well as opening the avenue of biological genetic engineering.
The conclusion of World War I and the resulting Treaty of Versailles saw the United Kingdom, France, Italy, the United States and Japan as the main arbiters of the new world order. Germany returned as a great power in 1933, when the Nazi Party replaced the Weimar Republic as the new government of Germany.