The 20th century was a century that started on January 1, 1901, and ended on December 31, 2000. It was the tenth and last century of this 2nd century. It is distinct from the century known as the 1900s which began on January 1, 1900, and ended on December 31, 1999.
The 20th century has been dominated by a chain of events that heralded significant changes in history regarding redefining the age: World War I and World War II, nuclear power and space exploration, nationalism and decolonization, the Cold War and post-Cold War conflicts; intergovernmental associations and cultural homogenization through developments from emerging transport and communications technologies; poverty reduction and world population increase, awareness of environmental degradation, environmental instability; along with the birth of the Digital Revolution. It saw great improvements in medical and communication technology that from the late 1980s permitted for near-instantaneous worldwide computer communication and genetic modification of existence.
Global overall fertility rates, sea level increase, and ecological collapses improved; the resulting competition for land and dwindling resources hastened deforestation, water depletion, and also the mass extinction of many of the planet‘s species and decline in the population of others; impacts which are presently being dealt with. It took all of human history around 1804 for the planet‘s population to reach 1 billion; world inhabitants attained an estimated two billion in 1927; from late 1999, the international population reached 6 billion. International literacy averaged 80 percent; global lifespan-averages exceeded 40+ years for the very first time in history, with over half achieving 70+ years (three decades longer than it was a century ago).
The century had the first global-scale absolute wars between world forces across continents and oceans in World War I and World War II. Nationalism became a major political issue in the world in the 20th century, also acknowledged in international law together with the appropriate of nations to self-determination, formal decolonization in the mid-century, and related regional battles.
The century saw a major shift in the manner that many people lived, with changes in politics, ideology, economics, society, civilization, science, technology, and medicine. The 20th century may have seen more scientific and technological progress than the rest of the centuries united since the dawn of civilization. Conditions like ideology, world war, genocide, and nuclear war entered common usage. Scientific discoveries, such as the theory of relativity and quantum physics, vastly altered the foundational models of physical science, forcing scientists to understand that the world was more complicated than previously believed, and dashing the hopes (or fears) at the end of the 19th century that the last few details of scientific knowledge were about to be filled in. It was a century that started with horses, simple automobiles, and freighters but finished with high-speed rail, cruise ships, global commercial air travel and also the Space Shuttle. Horses, Western society‘s basic form of private transportation for thousands of years, were replaced with automobiles and buses within a few decades. These improvements have been made possible by the manipulation of fossil fuel sources, which offered energy in an easily portable type but also caused concern about pollution and long-term impact on the surroundings. Humans explored space for the first time, carrying their very first footsteps on the Moon.