20Th century

The British, Chinese, Russian, German, Ottoman, and Austro-Hungarian empires dissolved in the first half of the century, with all but the British, French, and Japanese empires collapsing during thecourse of World War I. The inter-war years saw a Great Depression cause a massive disruption to the world economy. Shortly afterwards, World War II broke out, putting the Allied powers (chiefly theSoviet Union, the United Kingdom, and the United States) against the Axis powers (chiefly Nazi Germany, the Empire of Japan, and Italy) which eventually resulted in a total victory for the Allies, at thecost of over 60 million lives and the complete devastation of many nations. As a means of preventing future world wars, the United Nations was formed; however, competition between the two newsuperpowers, the Soviet Union and the United States, resulted in the Cold War, which would dominate geopolitical life for the next 45 years. The Soviet Union collapsed internally in 1991, resulting in theUnited States taking on sole superpower status, although by the end of the century China, India, and the European Union had greatly increased their influence.

The century saw a major shift in the waythat vast numbers of people lived, as a result of changes in politics, ideology, economics, society, culture, science, technology, and medicine. Terms like ideology, world war, genocide, and nuclearwar entered common usage. Scientific discoveries, such as the theory of relativity and quantum physics, drastically changed the worldview of scientists, causing them to realize that the universe wasfantastically more complex than previously believed, and dashing the hopes at the end of the 19th century that the last few details of scientific knowledge were about to be filled in. Acceleratingscientific understanding, more efficient communications, and faster transportation transformed the world in those hundred years more rapidly and widely than in any previous century. It was a century...