Key events of the 20th century

The war was precipitated by the Assassination in Sarajevo of the Austro-Hungarian Empire's heir to the throne, Erzherzog Franz Ferdinand, by Gavrilo Princip, a member of the Young Bosnia liberation movement.

[12] An international body called the League of Nations was formed to mediate disputes and prevent future wars, although its effectiveness was severely limited by, among other things, its reluctance and inability to act.

[14] However, the European revolutions were defeated, Vladimir Lenin died in 1924, and within a few years, Joseph Stalin displaced Leon Trotsky as the de facto leader of the Soviet Union.

[19] The responses to the crisis often made the situation worse, as millions of people watched their savings become next to worthless, and the idea of a steady job with a reasonable income fading away.

This treaty gave Stalin free rein to take the Baltic republics of Estonia, Latvia, and Lithuania, as well as Eastern Poland, all of which would remain in Soviet possession after the war.

[37] Stalin also launched an attack on Finland, which he hoped to reduce to little more than a Soviet puppet state, but the Red Army met staunch Finnish resistance in what became known as the Winter War and succeeded in gaining only limited territory from the Finns.

[68] By this time, Rommel had been forced to abandon North Africa after a defeat by Montgomery at El Alamein in what was the first decisive victory of the Allies over the Germany army, leading Churchill to declare it "the end of the beginning".

In the winter of 1944, Hitler put everything into one last desperate gamble in the West, known as the Battle of the Bulge, which, despite an initial advance, was a failure, because the introduction of new Allied tanks and low troop numbers among the Germans prevented any real action being taken.

However, the Supreme Allied Commander, American general Dwight D. Eisenhower, refused to strike for Berlin, and instead became obsessed with reports of possible guerrilla activity in southern Germany, which in reality existed mainly in the propaganda of Joseph Goebbels.

The first event that is usually linked to the later Pacific conflict was the Mukden Incident of 18 September 1931, during which the Japanese military staged the bombing of the South Manchuria Railway and pinned the blame on Chinese dissidents.

Following Chinese victories in Changsha and Guangxi in 1939, the war reached somewhat of a stalemate, with Japan controlling the large cities, but being unable to rule the vast countryside.

[95] On 7 December 1941, Japan launched a surprise attack on the American base at Pearl Harbor as a mean of preventing the U.S. Pacific Fleet from interfering with its planned expansion in the area.

[97][98] At the same time, Japan also launched attacks on Thailand, the British colonies of Malaya, Singapore, Hong Kong and American military bases in Guam, Wake Island and the Philippines.

[105] The losses suffered during this Battle of Midway, paired with the campaign of attrition that was taking place in Solomon Islands, left Japan unable to replenish its forces and turned the tides of war against it.

[106] Over the next two years the Allies slowly captured one island base after another, trying to get closer to Japan itself, where it planned to launch massive strategic air attacks and, only if absolutely necessary, execute a ground invasion.

[107] Despite the advances of the Allies, massive fighting was still taking place, both in South-East Asia with the Japanese offensive in India and in the Pacific, with the Battle of the Philippine Sea, where Japan suffered major losses and definitively lost the ability to rely on aircraft carriers.

[112] Despite the American troops outnumbering the Japanese to a rate of more than 3 to 1, the USA suffered heavy casualties in the 36 days of fighting, with over 6,800 Marines killed and another 20,000 wounded,[113] leading some historians to question the strategic worth of the action.

[114] With Japan struggling to defend the homeland islands, counteroffensives in other parts of the Japanese Empire became more feasible, with important battles taking place in Burma, Borneo and China.

[123] The Holocaust (which roughly means "great fire") was the deliberate, systematic murder of millions of Jews and other minorities during World War II by Hitler's Nazi regime in Europe.

[131][132] Not only were Jews shot or gassed to death en masse, but they were forced to provide slave labor and they were used in horrific medical experiments (see Human experimentation in Nazi Germany).

[175] Through the efforts of Amílcar Cabral and others, the Portuguese colonies of Guinea-Bissau, Cape Verde, Angola, Mozambique and São Tomé and Príncipe followed suit and achieved independence during the mid-1970s, in what was to be the last important wave of African decolonization.

[178] In many cases this meant that historically antagonistic ethnic or religious groups now needed to share the same country or that several nations held territorial claims over regions which were more or less arbitrarily divided by European powers.

[181] During the Yalta Conference, where the Western, capitalist powers, and the communist Soviet Union agreed on separate spheres of influence in Europe, they set up the stage for a geopolitical rivalry that would dominate international relations for the next five decades.

[189] The spread of the communist ideology in general and the Soviet influence in particular made Western leaders nervous and it even lead to Churchill considering a preemptive attack on the USSR even before World War II was formally ended.

However, the war reached a stalemate after Chinese intervention pushed U.N. forces back, and an Armistice ended hostilities in July 1953, leaving the two Koreas divided and tense for the rest of the century.

The plan went awry, with Nixon deliberately sabotaging peace talks for political gain,[202] and the war spilled into neighboring Cambodia while South Vietnamese forces were pushed further back.

[250][251] The main impetus for this was electronic mail, a far faster and convenient form of communication than a conventional letter and memo distribution, and the File Transfer Protocol (FTP).

With the end of colonialism and the Cold War, nearly a billion people in Africa were left with truly independent new nation-states, some cut from whole cloth, standing up after centuries of foreign domination.

Meanwhile in South Africa, the apartheid came to an end and Nelson Mandela became the nation's first black president, leading to the formation of a new democratic government, after having being ruled for four and a half decades of systemised racial segregation.

The most serious problem was global warming, which was predicted to frequently flood coastal areas, due to human-caused emission of greenhouse gases, particularly carbon dioxide produced by the burning of fossil fuels.