The century had the first global-scale total wars between world powers 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, acknowledged in international law along with the right of nations to self-determination, official decolonization in the mid-century, and related regional conflicts.
The century saw a major shift in the way that many people lived, with changes in politics, ideology, economics, society, culture, science, technology, and medicine. The 20th century may have seen more technological and scientific progress than all the other centuries combined since the dawn of civilization. Terms like ideology, world war, genocide, and nuclear war entered common usage. Scientific discoveries, such as the theory of relativity and quantum physics, profoundly changed the foundational models of physical science, forcing scientists to realize that the universe was more complex 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 ended with high-speed rail, cruise ships, global commercial air travel and the Space Shuttle. Horses, Western society's basic form of personal transportation for thousands of years, were replaced by automobiles and buses within a few decades. These developments were made possible by the exploitation of fossil fuel resources, which offered energy in an easily portable form, but also caused concern about pollution and long-term impact on the environment. Humans explored space for the first time, taking their first footsteps on the Moon.
World powers and empires in 1914, just before the First World War
Mass media, telecommunications, and information technology (especially computers, paperback books, public education, and the Internet) made the world's knowledge more widely available. Advancements in medical technology also improved the health of many people: the global life expectancy increased from 35 years to 65 years. Rapid technological advancements, however, also allowed warfare to reach unprecedented levels of destruction. World War II alone killed over 60 million people, while nuclear weapons gave humankind the means to annihilate itself in a short time. However, these same wars resulted in the destruction of the imperial system. For the first time in human history, empires and their wars of expansion and colonization ceased to be a factor in international affairs, resulting in a far more globalized and cooperative world. The last time major powers clashed openly was in 1945, and since then, violence has seen an unprecedented decline.
The world also became more culturally homogenized than ever with developments in transportation and communications technology, popular music and other influences of Western culture, international corporations, and what was arguably a truly global economy by the end of the 20th century.
Technological advancements during World War I changed the way war was fought, as new inventions such as tanks, chemical weapons, and aircraft modified tactics and strategy. After more than four years of trench warfare in Western Europe, and 20 million dead, the powers that had formed the Triple Entente (France, Britain, and Russia, later replaced by the United States and joined by Italy and Romania) emerged victorious over the Central Powers (Germany, Austria-Hungary, the Ottoman Empire and Bulgaria). In addition to annexing many of the colonial possessions of the vanquished states, the Triple Entente exacted punitive restitution payments from them, plunging Germany in particular into economic depression. The Austro-Hungarian and Ottoman empires were dismantled at the war's conclusion. The Russian Revolution resulted in the overthrow of the Tsarist regime of Nicholas II and the onset of the Russian Civil War. The victorious Bolsheviks then established the Soviet Union, the world's first communist state.
At the beginning of the period, the British Empire was the world's most powerful nation, having acted as the world's policeman for the past century. Fascism, a movement which grew out of post-war angst and which accelerated during the Great Depression of the 1930s, gained momentum in Italy, Germany, and Spain in the 1920s and 1930s, culminating in World War II, sparked by Nazi Germany's aggressive expansion at the expense of its neighbors. Meanwhile, Japan had rapidly transformed itself into a technologically advanced industrial power and, along with Germany and Italy, formed the Axis powers. Japan's military expansionism in East Asia and the Pacific Ocean brought it into conflict with the United States, culminating in a surprise attack which drew the US into World War II. After some years of dramatic military success, Germany was defeated in 1945, having been invaded by the Soviet Union and Poland from the East and by the United States, the United Kingdom, Canada, and France from the West. After the victory of the Allies in Europe, the war in Asia ended with the dropping of two atomic bombs on Japan by the US, the first nation to develop and use nuclear weapons. In total, World War II left some 60 million people dead. After the war, Germany was occupied and divided between the Western powers and the Soviet Union. East Germany and the rest of Eastern Europe became Soviet puppet states under communist rule. Western Europe was rebuilt with the aid of the American Marshall Plan, resulting in a major post-war economic boom, and many of the affected nations became close allies of the United States.
With the Axis defeated and Britain and France rebuilding, the United States and the Soviet Union were left standing as the world's only superpowers. Allies during the war, they soon became hostile to one another as their competing ideologies of communism and democratic capitalism proliferated in Europe, which became divided by the Iron Curtain and the Berlin Wall. They formed competing military alliances (NATO and the Warsaw Pact) which engaged in a decades-long standoff known as the Cold War. The period was marked by a new arms race as the USSR became the second nation to develop nuclear weapons, which were produced by both sides in sufficient numbers to end most human life on the planet had a large-scale nuclear exchange ever occurred. Mutually assured destruction is credited by many historians as having prevented such an exchange, each side being unable to strike first at the other without ensuring an equally devastating retaliatory strike. Unable to engage one another directly, the conflict played out in a series of proxy wars around the world–particularly in China, Korea, Vietnam, and Afghanistan–as the USSR sought to export communism while the US attempted to contain it. The technological competition between the two sides led to substantial investment in research and development which produced innovations that reached far beyond the battlefield, such as space exploration and the Internet.
In the latter half of the century, most of the European-colonized world in Africa and Asia gained independence in a process of decolonization. Meanwhile, globalization opened the door for several nations to exert a strong influence over many world affairs. The US's global military presence spread American culture around the world with the advent of the Hollywood motion picture industry, Broadway, rock and roll, pop music, fast food, big-box stores, and the hip-hop lifestyle. Britain also continued to influence world culture, including the "British Invasion" into American music, leading many rock bands from other countries (such as Swedish ABBA) to sing in English. After the Soviet Union collapsed under internal pressure in 1991, most of the communist governments it had supported around the world were dismantled—with the notable exceptions of China, North Korea, Cuba, Vietnam, and Laos—followed by awkward transitions into market economies.
Following World War II, the United Nations, successor to the League of Nations, was established as an international forum in which the world's nations could discuss issues diplomatically. It enacted resolutions on such topics as the conduct of warfare, environmental protection, international sovereignty, and human rights. Peacekeeping forces consisting of troops provided by various countries, with various United Nations and other aid agencies, helped to relieve famine, disease, and poverty, and to suppress some local armed conflicts. Europe slowly united, economically and, in some ways, politically, to form the European Union, which consisted of 15 European countries by the end of the 20th century.
In the last third of the century, concern about humankind's impact on the Earth's environment made environmentalism popular. In many countries, especially in Europe, the movement was channeled into politics through Green parties. Increasing awareness of global warming began in the 1980s, commencing decades of social and political debate.
is a major technological advancement in this century.
The nature of innovation and change
Due to continuing industrialization and expanding trade, many significant changes of the century were, directly or indirectly, economic and technological in nature. Inventions such as the light bulb, the automobile, and the telephone in the late 19th century, followed by supertankers, airliners, motorways, radio, television, antibiotics, nuclear power, frozen food, computers and microcomputers, the Internet, and mobile telephones affected people's quality of life across the developed world. Scientific research, engineering professionalization and technological development—much of it motivated by the Cold War arms race—drove changes in everyday life.
At the beginning of the century, strong discrimination based on race and sex was significant in general society. Although the Atlantic slave trade had ended in the 19th century, the fight for equality for non-white people in the white-dominated societies of North America, Europe, and South Africa continued. During the century, the social taboo of sexism fell. By the end of the 20th century, women had the same legal rights as men in many parts of the world, and racism had come to be seen as abhorrent. Attitudes towards homosexuality also began to change in the later part of the century.
The world at the end of the 20th century
Communications and information technology, transportation technology, and medical advances had radically altered daily lives. Europe appeared to be at a sustainable peace for the first time in recorded history. The people of the Indian subcontinent, a sixth of the world population at the end of the 20th century, had attained an indigenous independence for the first time in centuries. China, an ancient nation comprising a fifth of the world population, was finally open to the world, creating a new state after the near-complete destruction of the old cultural order. With the end of colonialism and the Cold War, nearly a billion people in Africa were left in new nation states after centuries of foreign domination.
The world was undergoing its second major period of globalization; the first, which started in the 18th century, having been terminated by World War I. Since the US was in a dominant position, a major part of the process was Americanization. The influence of China and India was also rising, as the world's largest populations were rapidly integrating with the world economy.
Terrorism, dictatorship, and the spread of nuclear weapons were pressing global issues. The world was still blighted by small-scale wars and other violent conflicts, fueled by competition over resources and by ethnic conflicts. Despots such as Kim Jong-il of North Korea continued to lead their nations toward the development of nuclear weapons.
Disease threatened to destabilize many regions of the world. New viruses such as SARS and West Nile 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 may threaten the planet's habitability. 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.