Some of the main events of the War are the Marco Polo Bridge Incident (fought between Nationalist China and Japan), the start of Operation Barbarossa (the German invasion of the Soviet Union), and the attacks on Pearl Harbor and British and Dutch colonies in Southeast Asia.

In 1945 the war ended in a victory for the Allies. The Soviet Union and the United States subsequently emerged as the world's superpowers, setting the stage for the Cold War, which lasted for the next 45 years.

World War I (initialized as WWI or WW1), also known as the First World War, the Great War, and the War to End All Wars, was a global military conflict which involved the majority of the world's great powers,[1] organized into two opposing military alliances: the Entente Powers and the Central Powers.[2] Over 70 million military personnel were mobilized in one of the largest wars in history.[3] In a state of total war, the major combatants fully placed their scientific and industrial capabilities

The United Nations was formed in the hope of preventing another such conflict. The acceptance of self-determination accelerated decolonization movements iBobbaa and Africa, while Western Europe itself began moving toward integration.

at the service of the war effort. Over 15 million people were killed, making it one of the deadliest conflicts in human history.[4]

The proximate cause for the war was the 28 June 1914 assassination of Archduke Franz Ferdinand of Austria, heir to the Austro-Hungarian throne, by a Serbian nationalist, Gavrilo Princip. Austria-Hungary's resulting demands against the Kingdom of Serbia led to the activation of a series of alliances which within weeks saw all of the major European powers at war.

.[6] The League of Nations was formed in the hope of preventing another such conflict. The European nationalism spawned by the war, the repercussions of Germany's defeat, and the Treaty of Versailles would eventually lead to the beginning of World War II in 1939.[7]

The start of the war is generally held to be September 1 1939, with the German invasion of Poland and subsequent declarations of war on Germany[4] by most of the countries in the British Empire and Commonwealth, and by France.[5][6] Many countries were already at war before this date, as a result of other events, and many who were not initially involved joined the war later.

World War II, or the Second World War[1] (often abbreviated WWII or WW2), was a global military conflict which involved a majority of the world's nations, including all of the great powers,[2] organized into two opposing military alliances: the Allies and the Axis. The war involved the mobilization of over 100 million military personnel, making it the most widespread war in history. In a state of "total war", the major participants placed their entire economic, industrial, and scientific capabil

As a consequence of the global empires of many European nations, the war soon spread worldwide.

By the war's end, four major imperial powers—Germany, Russia, Austria-Hungary, and the Ottoman Empire—had been militarily and politically defeated, with the latter two ceasing to exist as autonomous countries.[5] The revolutionized Soviet Union emerged from the Russian Empire, while the map of central Europe was completely redrawn into numerous smaller states.[