The 20th century lasted from 1901 to 2000 in the Gregorian calendar. Common usage sometimes regards it as lasting from 1900 to 1999, but this is considered incorrect due to the nonexistence of a "Year Zero" before AD 1. The 20th century is also sometimes known as the nineteen hundreds (1900s), referring to the latter usage. Decades are almost always considered as starting with the "0" year and named accordingly ("1960s", etc.), so the first decade of a century technically overlaps back into the preceding one.
The twentieth century saw a remarkable shift in the way that vast numbers of people lived, as a result of technological, medical, social, ideological, and political innovations. Terms like ideology, world war, genocide, and nuclear war entered common usage, and became an influence on the lives of everyday people. War reached an unprecedented scale and level of sophistication, approximately 57 million people died as a result of the Second World War (1939-1945) alone. The trends of mechanization of goods and services and networks of global communication, which were begun in the 19th century, continued at an ever-increasing pace in the 20th. In spite of the terror and chaos, the 20th century saw many attempts at world peace. As the 35th President of the United StatesJohn F. Kennedy said:
What kind of peace do we seek? I am talking about a genuine peace, the kind of peace that makes life on earth worth living. Not merely peace in our time, but peace in all time. Our problems are man-made, therefore they can be solved by man. For in the final analysis, our most basic common link is that we all inhabit this small planet, we all breath the same air, we all cherish our children's future, and we are all mortal.
Virtually every aspect of life in virtually every human society changed in some fundamental way or another during the twentieth century.
The 20th century has sometimes been called, both within and outside the United States, the American Century, though this is a controversial term.
Important developments, events and achievements
Science and technology
The assembly line and mass production of motor vehicles and other goods allowed manufacturers to produce more and cheaper products. This allowed the automobile to become the most important means of transportation.
The economic and political aftermath of World War I led to the rise of Fascism and Nazism in Europe, and shortly to World War II. This war also involved Asia and the Pacific, in the form of Japanese aggression against China and the United States. While the First World War mainly cost lives among soldiers, civilians suffered greatly in the Second -- from the bombing of cities on both sides, and in the unprecedented German genocide of the Jews and others, known as the Holocaust.
Movies, music and the media had a major influence on fashion and trends in all aspects of life. As many movies and music originate from the United States, American culture spread rapidly over the world.
After gaining political rights in the United States and much of Europe in the first part of the century, women became more independent throughout the century.
The automobile provided vastly increased transportation capabilities for the average member of Western societies in the early to mid-century, spreading even further later on. City design throughout most of the West became focused on transport via car. The car became a leading symbol of modern society, with styles of car suited to and symbolic of particular lifestyles.
Sports became an important part of society, becoming an activity not only for the privileged. Watching sports, later also on television, became a popular activity.
Disease and medicine
Although the availability and quality of medicine continued to improve, epidemic diseases continued to spread, aided by modern transportation. An influenza pandemic, the Spanish Flu, killed 25 million between 1918 and 1919, while AIDS is yet uncured and treatments remain too expensive for wide use in developing countries.
The widespread use of petroleum in industry -- both as a chemical precursor to plastics and as a fuel for the automobile and airplane -- led to the vital geopolitical importance of petroleum resources. The Middle East, home to many of the world's oil deposits, became a center of geopolitical and military tension throughout the latter half of the century.
A vast increase in fossil fuel consumption leads to depletion of natural resources, while air pollution possibly leads to global warming and the ozone hole. The problem is increased by world-wide deforestation, also causing a loss of biodiversity. The problem of a depletion of natural resources is decreased by advances in drilling technology which led to a net increase in the amount of fossil fuel that is readily obtainable at the end of the century, as compared with the amount considered obtainable at the beginning of the century.