How does first world war lead to second world war ?

 World War II, or the Second World War (often abbreviated as WWII or WW2), was a global military conflict lasting from 1939 to 1945, which involved most of the world's nations, including all of the great powers, organized into two opposing military alliances: the Allies and the Axis. It was the most widespread war in history, with more than 100 million military personnel mobilized. In a state of "total war," the major participants placed their entire economic, industrial, and scientific capabilities at the service of the war effort, erasing the distinction between civilian and military resources. Marked by significant events involving the mass death of civilians, including the Holocaust and the only use of nuclear weapons in warfare, it was the deadliest conflict in human history, resulting in 50 million to over 70 million fatalities.

The war is generally accepted to have begun on 1 September 1939, with the invasion of Poland by Germany declarations of war on Germany by France and most of the countries of the British Empire Common wealth. Germany set out to establish a large German empire in Europe. During 1939 to early 1941, in a series of successful military campaigns and political treaties, Germany conquered or politically subdued most of continental Europe apart from the Soviet Union. Britain and the Commonwealth remained the only major force continuing the fight against the Axis in North Africa and in extensive naval warfare. In June 1941, the European Axis launched an invasion of the Soviet Union, giving a start to the largest land theatre of war in history, which, from this moment on, was tying down the major part of the Axis military power. In December 1941, Japan, which had already been at war with China since 1937, and which aimed to establish a dominance over East Asia and Southeast Asia, attacked the United States and European possessions in the Pacific Ocean, quickly conquering a significant part of the region. 

The Axis advance was stopped in 1942 after the defeat of Japan in a series of naval battles and after devastating defeats of European Axis troops in North Africa and at Stalingrad. In 1943, with a series of German defeats in Eastern Europe, the Allied invasion of Fascist Italy, and American victories in the Pacific, the Axis had lost strategic initiative and passed to strategic retreat on all fronts. In 1944, the Western Allies invaded France, whereas the Soviet Union regained all territorial losses and invaded the territory of Germany and its allies. The war in Europe ended with the capture of Berlin by Soviet troops and subsequent German unconditional surrender on 8 May 1945. By that time, the Japanese Navy was defeated by the United States, and invasion of the Japanese Archipelago ("Home Islands") became imminent.

The war ended with the total victory of the Allies over Germany and Japan in 1945. World War II left the political alignment and social structure of the world significantly altered. While the United Nations (UN) was established to foster international cooperation and prevent future conflicts (such as World War III), the Soviet Union and the United States emerged as rival superpowers, setting the stage for the Cold War, which would last for the next 46 years. Meanwhile, the influence of European great powers started to decline, while the decolonization of Asia and of Africa began. Most countries whose industries had been badly damaged began moving toward economic recovery and across the world political integration emerged in an effort to peacefully stabilize after-war relations.

How was the World War First Started ?

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World War I was a military conflict centered on Europe that began in the summer of 1914. The fighting ended in late 1918. This conflict involved all of the world's great powers, assembled in two opposing alliances: the Allies (centered around the Triple Entente) and the Central Powers. More than 70 million military personnel, including 60 million Europeans, were mobilized in one of the largest wars in history .More than 9 million combatants were killed, due largely to great technological advances in firepower without corresponding ones in mobility. It was the second deadliest conflict in history.

The term World War One is particularly common in American English, whereas in Britain and the The Commonwealth, it is more commonly called the First World War. This term was first coined in 1920 as the title of Charles a Court Pennington's book, but references to it being the first war did not become popular until World War II. The terms World War One and Two were first used in Time magazine in 1938. During and in the aftermath of the conflict it was called the Great War, particularly in British newspapers, whereas US media preferred simply the World War. It was also known as the War to End All Wars.

The assassination on 28 June 1914 of Archduke Franz Ferdinand of Austria, the heir to the throne of Austria-Hungary, is seen as the immediate trigger of the war. Long-term causes, such as imperialistic foreign policies of the great powers of Europe, such as the German Empire, the Austro-Hungarian Empire, the Ottoman Empire, the Russian Empire, the British Empire, France, and Italy, played a major role. Ferdinand's assassination by a Yugoslav nationalist resulted in a Habsburg ultimatum against the Kingdom of Serbia.colonies, the conflict soon spread around the world. Several alliances formed over the past decades were invoked, so within weeks the major powers were at war; as all had On 28 July the conflict opened with the Austro-Hungarian invasion of Serbia, followed by the German invasion of Belgium, Luxembourg and France; and a Russian attack against Germany. 

After the German march on Paris was brought to a halt, the Western Front settled into a static battle of attrition with a trench line that changed little until 1917. In the East, the Russian army successfully fought against the Austro-Hungarian forces but was forced back by the German army. Additional fronts opened after the Ottoman Empire joined the war in 1914, Italy and Bulgaria in 1915 and Romania in 1916. The Russian Empire collapsed in 1917, and Russia left the war after the October Revolution later that year. After a 1918 German offensive along the western front, United States forces entered the trenches and the allies drove back the German armies in a series of successful offensives. Germany agreed to a cease fire on 11 November 1918, later known as Armistice Day.

By the war's end, four major imperial powers—the German, Russian, Austro-Hungarian and Ottoman Empires—had been militarily and politically defeated. The last two ceased to exist. The revolutionized Soviet Union emerged from the Russian Empire, while the map of central Europe was completely redrawn into numerous smaller states. The League of Nations was formed in the hope of preventing another such conflict. The European nationalism spawned by the war and the break-up of empires, and the repercussions of Germany's defeat and the 

Treaty of Versailles led to the beginning of World War II in 1939.