The 20th century started on January 1, 1901 and ended on December 31, 2000, according to the Gregorian calendar. A common belief is that it started in 1900 and ended in 1999. Some historians consider the era from about 1914 to 1992 to be the Short Twentieth Century. The twentieth century was a period of radical departure in the way almost every human activity had been done in the past. Accelerating scientific understanding, better communications, faster transportation transformed the world in those hundred years more than any time in the past. It was a century that started with steam powered ships as the most sophisticated means of transport, and ended with the space shuttle. Horses, and other pack animals, Western humanity's basic form of personal transportation for thousands of years were replaced by automobiles within the span of a few decades. 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 innovation. Arguably more technological advances occurred in any 10 year period following World War I than the sum total of new technological development in any previous century. 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; in the Second World War (1939-1945) alone, approximately 57 million people died, mainly due to massive improvements in weaponry. 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. Virtually every aspect of life in virtually every human society changed in some fundamental way or another during the twentieth century and for the first time, any individual could influence the course of history no matter their background. Arguably, the 20th century re-shaped the face of the planet in more ways than any previous century. * Technology * Death rates * Infant mortality * Infectious disease * Life expectancy * Maternal death rates * Battles Scientific discoveries such as relativity and quantum physics radically changed the worldview of scientists, causing them to realize that the universe was much more complex than they had previously believed, and dashing the hopes at the end of the preceding century that the last few details of knowledge were about to be filled in. For a more coherent overview of the historical events of the century, see The 20th century in review. The 20th century has sometimes been called, both within and outside the United States, the American Century, though this is a controversial term. Science and Technology Ford assembly line, 1913 Enlarge Ford assembly line, 1913 * 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 invention of fixed-wing aircraft and the jet engine allowed for the world to become "smaller." Space flight increased knowledge of the rest of the universe and allowed for global real-time communications via geosynchronous satellites. * Mass media technologies such as film, radio, and television allow the communication of political messages and entertainment with unprecedented impact * Mass availability of the telephone and later, the computer, especially through the Internet, provides people with new opportunities for near-instantaneous communication * Applied electronics, notably in its miniaturized form as integrated circuits, made possible the above mentioned rise of mass media, telecommunications, ubiquitous computing, and all kinds of "intelligent" appliances; as well as many advances in natural sciences such as physics, by the use of exponentially growing calculation power (see supercomputer). * The development of Nitrogen fertilizer, insecticides and herbicides resulted in significantly higher agricultural yield. Chemical warfare is massively used in World War I. * Advances in fundamental physics through the theory of relativity and quantum mechanics led to the development of nuclear weapons (known informally as "the Bomb" and dropped on the industrial town of Hiroshima and the historic town of Nagasaki), the nuclear reactor, the semiconductor and the laser. Quantum mechanics also led to the development of applied electronics, radiation therapy, and synthesis of many new chemicals, including antibiotics and plastics. Fusion power was studied extensively but remained an experimental technology at the end of the century. * Inventions such as the washing machine and air conditioning led to an increase in both the quantity and quality of leisure time for the middle class in developed countries. * Most influential inventions in the 20th century: antibiotics, oral contraceptives, new plastics, transistors, Internet