After a long, uneasy peace in Europe, World War I was touched off by the assassination of  Francis-Ferdinand, heir to the throne of Austria-Hungary. Shortly thereafter, Austria-Hungary declared war on Serbia, causing Russia to mobilize. Alarmed, Germany issued ultimatums to Russia and France, and then declared war on both countries. This brought Great Britain into the war. The combined forces of Germany, Austria-Hungary, and Italy fought against Great Britain, France, and Russia. Eventually America entered the combat in aid of the latter countries and helped them win the war.

https://www.history.com/topics/world-war-i/world-war-i-history

http://www.bbc.co.uk/history/worldwars/wwone

1915 C.E.
The Twenty-One Demands

Using World War I as a distraction, Japanese diplomats secretly pressed China to accept 21 demands, making it clear that if China refused, war would result. In effect, these concessions made China a protectorate of Japan, solidifying Japan's position as a world power.

https://www.britannica.com/event/Twenty-one-Demands

As World War I raged, internal stresses in Russia intensified. The Duma appointed a government without tsarist approval, and in March 1917, Nicholas II abdicated. In October 1917, the Bolsheviks, a radical party led by Vladimir Lenin, seized power from the existing government. (In 1918, Nicholas and his family were murdered on Lenin's orders.) Lenin eradicated the traditional class system and established the Communist Party, which controlled all production, ownership, and political life in Russia and the future Soviet Union.

https://encyclopedia.ushmm.org/content/en/article/the-russian-revolution-1917

After British victories in the Middle East, Arthur Balfour, the British Foreign Minister, wrote a letter calling for a Jewish national home in Palestine. This declaration indicated Great Britain's favorable attitude toward establishing the state of Israel (which did not occur until after World War II, in 1948).

https://www.history.com/topics/middle-east/balfour-declaration

At the end of World War I, France, Great Britain, and the United States brokered this treaty, in which Germany lost much of its land and all its overseas colonies, and was required to reduce its military. The treaty's Clause 231 required Germany to admit responsibility for starting the war and pay heavy reparations to France and Belgium. Other treaties were signed at this time, in which Austria-Hungary was divided into two nations, and Bulgaria ceded lands to Yugoslavia. The terms of the treaty angered Germans.

https://history.state.gov/milestones/1914-1920/paris-peace

http://www.fordham.edu/halsall/mod/1919versailles.html

1919-1933 C.E.
The Weimar Republic

After World War I, elections took place in Germany to establish a democratic republic with a constitution. Its governing body, the National Assembly, met in Weimar, presiding over a country wracked by inflation and split by political dissension. As the Weimar government faltered, Adolf Hitler's National Socialist (Nazi) Party rose to prominence.

http://en.wikipedia.org/wiki/Weimar_Republic

http://weimar.facinghistory.org/content/why-study-weimar-germany

Turkish involvment in World War I was on the losing side. The Treaty of Sèvres formally ended the Ottoman Empire, compelling Turkey to relinquish most of its European territory and putting control of the Bosporus under Britain and France. Turkey's territory shrunk to a small part of Asia Minor, which was occupied by foreign troops. The conditions imposed on Turkey led to a Turkish nationalist movement.

http://www.gwpda.org/versa/sevres1.html

http://en.wikipedia.org/wiki/Treaty_of_Sevres

As cities and industries grew, the political leadership in Latin America countries tended to support urban workers instead of the landed elite. Latin American nations sought to limit outside intervention, especially that of the United States. Scroll down to see chapters 7 and 8 in the link below.

http://userpages.wittenberg.edu/mwood/borninbloodandfire.html

Egypt's independence movement had strengthened since the British occupation of 1882. In March 1919, the British deported three independence leaders; this set off an uprising that became a paralyzing strike. Egyptians rejected proposals for limited self-government. After further violent demonstrations, in February 1922, England unilaterally declared Egypt independent. In April a new constitution was approved and a law passed setting up parliamentary elections. However, British troops stayed on to protect Great Britain's interest in the Suez Canal.

http://countrystudies.us/egypt/28.htm

After World War I, war debt and a much-reduced workforce factored into rising economic and social stress in Italy. In 1914, a young journalist, Benito Mussolini, had founded a new fascist party. By 1922, his political power was such that he cabled King Vittorio Emmanuele II demanding to be made Prime Minister. The king and the social democratic government acceded, and on October 31, Mussolini became Italy's youngest prime minister. By combining propaganda, nationalist fervor, and force, he established a fascist dictatorship nearly a decade before Hitler's rise to power. In World War II, Italy allied itself with Germany, becoming one of the Axis powers.

http://cidc.library.cornell.edu/DOF/italy/italy.htm

http://www.euronet.nl/users/wilfried/ww2/mussolin.htm

Originally proposed as a treaty outlawing war between France and the United States, the Kellogg-Briand Pact (also known as the Pact of Paris) generally outlawed war. Signed by 15 nations, it was eventually ratified by 62 nations, but it provided no enforcement measures and was meaningless in practice. The pact did not prevent undeclared wars on the part of Japan, Italy, and Germany in the 1930s, for example.

https://history.state.gov/milestones/1921-1936/kellogg

1928-1953 C.E.
Stalin's U.S.S.R.

Joseph Stalin became Secretary General of the Soviet Union's Communist Party through ruthless infighting. Once in control, he accelerated industrial productivity in a series of Five-Year Plans; collectivized Soviet agriculture, killing about 14 million as farm yields dropped and famine struck; and rearmed the Soviet military. He instituted a policy of coercion and terror based on the Cheka, the Soviet secret police, and the Gulag, a network of state concentration camps. He ruled the U.S.S.R. until his death in 1953.

http://en.wikipedia.org/wiki/Joseph_Stalin

https://www.biography.com/dictator/joseph-stalin

Within eight weeks in 1929, stocks lost over 40 percent of their value, reaching bottom on October 29, the day the stock market crashed. The crash ushered in a more widespread economic depression that would sweep the United States and affect most of the industrialized world, causing bank failures and mass unemployment. Although President Franklin Roosevelt's New Deal policy helped blunt the economy's worst failures, it was not until the United States mobilized for the Second World War that the depression finally ended.

http://www.history.com/topics/great-depression

In 1930, India's Mohandas Gandhi began a campaign of civil disobedience towards British rule. Focusing on the Salt Act, which required Indians to buy salt from the colonial government, Gandhi led a march to the sea, where Indians would collect their own salt. Thousands joined the march, and the British launched reprisals. As world opinion began to align with Gandhi, representatives of the Crown met with him in 1931. They agreed to withdraw oppressive laws and not to prosecute protestors. Indian independence, achieved in 1947, was greatly spurred by the 1930 resistance.

http://history.com/topics/salt-march

Established in 1931, the Commonwealth of Nations, the successor to the British Empire, is a voluntary association of nations once governed by Great Britain as colonies.

http://geography.about.com/od/politicalgeography/
a/commonwealth.htm

When he took office, President Franklin D. Roosevelt announced a policy of nonintervention toward Latin American nations, in an attempt to distance the United States from previous US military actions in the region that had fostered ill will.

https://history.state.gov/milestones/1921-1936/good-neighbor

http://en.wikipedia.org/wiki/Good_Neighbor_policy

Effects in Germany of the Great Depression and the resulting political turmoil aided Adolf Hitler's rise to power. In the early 1930s, the Nazi Party made steady gains in the ever-shifting German parliament, and in 1933, Hitler was elected Chancellor. Shortly after purging his Party of any rivals, he began a military buildup and enacted the anti-Jewish Nuremburg Laws, setting up a network of concentration camps. His Gestapo police suppressed any dissent. Hitler's first move in expanding Germany's borders was to send troops to the demilitarized Rhineland in 1936, in defiance of the Versailles Treaty.

https://www.history.com/topics/world-war-ii/nazi-party

In the late 1920s, Mao Tse-tung built up the Communist Red Army. Soon after, Chiang Kai-shek's Nationalists began a campaign against Mao's army. In 1934, Nationalist troops forced the Communists to flee. The Long March had started. Mao led some 80,000 Communist fighters on a 6,000-mile-long retreat. Despite the 10 percent survival rate of his men, Mao had cemented his position as the foremost Communist leader by virtue of his leadership.

http://www.history.com/this-day-in-history/the-long-march

In Nazi Germany, these laws placed heavy restrictions on the lives of Jews. Jews were excluded from German citizenship, universities, and state employment, and were forbidden to marry outside of their religion. In public, they were forced to wear the yellow Star of David identifying them as Jewish. Jewish businesses were officially boycotted. After the laws were passed, violence against Jews intensified, as on Kristallnacht ("the night of broken glass") in 1938, when Nazis destroyed Jewish shops and synagogues.

https://encyclopedia.ushmm.org/content/en/article/the-nuremberg-race-laws

Spain experienced extreme divisions between its right and left political wings in the 1930s. At the outset of the war, Spain was a republic; by the war's end, it was a dictatorship. The country was split into the Nationalists, led by General Francisco Franco, and the Loyalists, who supported the democratically elected republic. Franco received support and troops from the Nazis, who saw an opportunity to test new battle tactics and equipment. Franco emerged victorious; Spain lay in ruins.

https://encyclopedia.ushmm.org/content/en/article/spanish-civil-war

Earlier in 1938, Hitler had merged Germany with Austria, in what was known as the Anschluss. He then turned to the Sudetenland of Czechoslovakia, claiming oppression of Germans there. Czech allies France and England advanced the policy of appeasing Hitler's appetite for expansion by giving him control of northern Czechoslovakia. The Munich Pact, which was supposed to stop German expansion to the east, permitted immediate occupation by German troops. The next year, Hitler invaded Poland, Czechoslovakia's next-door neighbor. 

http://avalon.law.yale.edu/imt/munich1.asp

In 1939, having made a nonaggression pact with Stalin, Hitler invaded Poland. This act was essentially the first salvo of World War II. Germany proceeded to conquer most of Western Europe, until Allied air power prevented the invasion of England. Hitler's decision to invade the Soviet Union and the entry of the United States into the war in 1941 foretold the German army's ultimate defeat in 1945. Germany, Italy, and Japan formed an alliance called the Axis, while France, Great Britain, Russia, and the United States constituted the Allied powers.

http://www.digitalhistory.uh.edu/era.cfm?eraID=15&smtid=1

The Holocaust was the planned and methodical attempt by Hitler and his Nazi forces to exterminate the entire Jewish population of Europe. More than 12 million people died in concentration camps and were slaughtered in death camps, of whom half were Jews. Other victims included ethnic minorities such as Gypsies, people with disabilities, and those whom Hitler considered social deviants. The program of killing ended when Allied troops entered the camps in 1945.

https://encyclopedia.ushmm.org/content/en/
article/introduction-to-the-holocaust

On December 7, 1941, in an attempt to neutralize American sea power in the Pacific, Japan carried out a sneak aerial attack on the United States Navy Base in Pearl Harbor, Hawaii. The attack killed 2,403, of whom 68 were civilians, and wounded 1,178. Twenty-one ships of the US Pacific fleet were sunk or damaged. In the next few days, America entered World War II, declaring war on Japan on December 8, and on Germany on December 11.

http://memory.loc.gov/ammem/today/dec07.html

Known as the bloodiest battle in history, with one million casualties, Stalingrad was a turning point in the war. German forces reached Stalingrad in the summer of 1942. Although they captured much of the city, they became bogged down as fighting continued into winter. Badly outnumbered and hampered by snow and ice, the Germans surrendered on February 2, 1943. This was an important victory for the Allies psychologically: the formidable Nazi war machine had begun to crack.

http://www.historyofwar.org/articles/battles_stalingrad.html

http://en.wikipedia.org/wiki/Battle_of_Stalingrad

On June 6, 1944, Allied forces under the command of U.S. Army General Dwight Eisenhower invaded a 60-mile stretch of French shoreline in Normandy and opened a western front against the German occupation of Europe. D-Day involved the largest amphibious assault ever launched.

http://www.history.com/topics/world-war-ii/d-day

May 8, 1945 marked the unconditional surrender of German forces to the Allies. This was the end of World War II in Europe.

http://news.bbc.co.uk/onthisday/hi/dates/
stories/may/8/newsid_3580000/3580163.stm

On April 25, 1945, 50 nations met in San Francisco to draft a charter for the United Nations, an organization dedicated to international policy, resolution of international disputes, and overseeing the global fight against poverty, ignorance, and disease.

https://history.state.gov/milestones/1937-1945/un

August 15, 1945, marked the unconditional surrender of Japanese forces. President Harry Truman had dropped two atomic bombs, the first on Hiroshima and the second on Nagasaki, before the Japanese surrendered.

http://www.otr.com/vj.html

http://news.bbc.co.uk/onthisday/hi/dates/
stories/august/15/newsid_3581000/3581971.stm