World Wars

Death and destruction, trench warfare, and the Holocaust are just some of the images conjured up when you hear the words 'world war'. Read on to learn more about the definition of a world war, and examine the two major conflicts of the 20th century that we know as 'world wars': World War I and World War II.

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Table of contents

    World War Definition

    Contrary to the name, a world war does not mean that the whole world is at war, but rather the world's major superpowers are at war, or at least involved in some capacity.

    A world war is different from a (civil) war. The former includes several superpower nations, whereas the latter is a war between countries that are not considered superpowers, wars within a country, or between states or ethnicities. A world war is on a more global scale.

    World War Terms

    The term 'world war' has been used since the mid-19th century. The term 'first world war' was first used by Ernest Haeckel, a German biologist and philosopher, shortly after the start of World War I. He said;

    There is no doubt that the course and character of the feared “European War” will become the first world war in the full sense of the word.1

    The 'European War' he mentions, which we call World War I, is also known as 'The Great War'.

    World War History

    When asked about world wars, there is every chance that World War I, II, or both spring to mind. These are indeed the two major international conflicts of the early 20th century that we call 'world wars'.

    That said, some historians feel that other conflicts also earn the dubious title of being a world war. These include:

    World War III

    While there is no official World War III yet (luckily!), it is considered a future potential. During World War II, the atomic bombs on Hiroshima and Nagasaki (Japan) sparked great fear of nuclear warfare. Atomic bombs were made possible because of Albert Einstein's research and his 'e=mc2' equation. Einstein himself said:

    I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones.2

    With (political) unrest in/between several countries and technological advances, nuclear warfare on a global scale is a real threat, potentially turning into World War III (but let's hope it does not!).

    World War Three?

    During WWII, Britain, the US, and the Soviet Union worked on and produced atomic bombs. Britain aided the US, making the Soviet Union highly suspicious of the US as they were not on friendly terms to begin with. Initially, the US was afraid of a potential atomic bomb from Germany but eventually used it on two Japanese cities, Nagasaki and Hiroshima. This angered Joseph Stalin, and it was the beginning of a potentially nuclear Mexican stand-off that was the beginning of the Cold War. This changed the future of international warfare, and the Cold War teetered on the edge of a nuclear third world war.

    World Wars Timeline

    World War I and World War II each lasted for several years, and a lot happened during that time! Let's look at timelines for both World Wars.

    World War I Timeline

    Below, you will see some key events from World War I.

    World War I Timeline
    28 June 1914 The assassination of Austrian Archduke Franz Ferdinand. This was the primary catalyst for the start of World War I.

    World Wars Archduke Franz Ferdinand StudySmarterFig. 1 - Archduke Franz Ferdinand

    28 July 1914The outbreak of World War I. Austria-Hungary declared war on Serbia.
    6 September 1914The First Battle of the Marne (France) began. Both sides dug themselves in, setting the tone for the trench warfare that characterised the Western Front for the next four years. The battle ended on 12 September 1914.

    World Wars German soldiers in Marne StudySmarterFig. 2 - German soldiers in Marne

    17 February 1915Gallipoli Campaign (Ottoman Empire) began. This resulted in a catastrophe for the Allied forces, who withdrew on 9 January 1916.
    22 April 1915The Second Battle of Ypres (Belgium) began. Germany started the modern era of chemical warfare. The battle ended on 25 May 1915.
    21 February 1916The Battle of Verdun (France) began. This was the longest battle of World War I, ending on 18 December 1916.
    1 July 1916 The Battle of the Somme (France) began. This was one of the deadliest battles in recorded human history. The battle ended on 18 November 1916.
    15 March 1917The abdication of Tsar Nicholas II during the Russian Revolution meant the Romanov Dynasty was overthrown, resulting in the Tsar and his family's execution. This gave rise to the power of Vladimir Lenin and the Bolsheviks.

    World Wars Tsar Nicholas II StudySmarterFig. 3 - Tsar Nicholas II

    6 April 1917 The US declared war on Germany.
    31 July 1917The Third Battle of Ypres (Belgium), also known as the Battle of Passchendaele, began. The battle ended on 10 November 1917.
    11 November 1917Germany and the Allied Forces signed an armistice agreement, which stopped the fighting.
    28 June 1919The Treaty of Versailles, the crucial peace treaty of World War I, was signed, officially ending World War I.
    Table 1

    World War II Timeline

    Below are the key events of World War II.

    World War II Timeline
    30 January 1933Hitler became Chancellor of Germany, taking power with his Nazi Party.
    1 September 1939Germany invaded Poland. France and Britain declared war on Germany two days later, marking the beginning of World War II.
    26 May 1940The Battle of Dunkirk (France) commenced under the code name Operation Dynamo. The battle ended on 4 June 1940.

    World Wars British soldiers firing at a German aircraft, Dunkirk (France) StudySmarterFig. 4 - British soldiers firing at a German aircraft in Dunkirk (France)

    10 July 1940The Battle of Britain began. This was the first major military campaign fought by air forces. The battle ended on 31 October 1940.
    7 September 1940The Blitz, a German bombing campaign on the UK, started. It lasted until 11 May 1941.
    7 December 1941Japan attacked Pearl Harbor, Hawaii, involving the US officially in World War II.
    4 June 1942The Battle of Midway started. This was a major naval battle against Japanese forces. It lasted for four days, ending on 7 June 1942.
    23 October 1942The second Battle of El Alamein (Egypt). The battle ended on 11 November 1942 with a British victory, marking the beginning of the end of the Western Desert Campaign.
    6 June 1944The invasion of Normandy (France) in Operation Overlord. Known as D-Day, this was the largest seaborne invasion in history.
    16 December 1944The Battle of the Bulge (Ardennes: Belgium, Luxembourg, and Germany) was Germany's last major offensive campaign on the Western Front. Due to its location, it was also known as the Ardennes Offensive. The battle ended on 25 January 1945.
    30 April 1945Knowing there was no way to win and no way out, Hitler committed suicide.
    6 & 9 August 1945On 6 August, the atomic bomb 'Little Boy' was dropped on Hiroshima; on 9 August, the atomic bomb 'Fat Man' was dropped on Nagasaki, both in Japan.
    2 September 1945World War II ended.
    Table 2

    As mentioned earlier, both wars were extensive. Below, we will go into more detail.

    World War 1

    World War 1 (World War I, WWI, WW1), also known as the Great War, was a major conflict on a global scale. The primary catalyst for the war was the assassination of Austrian Archduke Franz Ferdinand (and his wife) on 28 June 1914 in Sarajevo (Bosnia Herzegovina). A month later, Austria-Hungary attacked Serbia, marking the beginning of WWI.

    The war was fought between the Central Powers of Germany, Austria-Hungary, Bulgaria, and the Ottoman Empire (nowadays Turkey) and the Allied Powers of Great Britain, Russia, France, Romania, Italy, Canada, Japan, and the US; both joined by their respective supporters.

    Germany started fighting on two fronts: France in the west and Russia in the east.

    During the First Battle of the Marne, France (6 September - 12 September 1914), forces on both sides dug trenches, setting the tone for the rest of the war.

    Significant battles during WWI are the Second Battle of Ypres (22 April 1915 - 25 May 1915), the Battle of Verdun (21 February 1916 - 18 December 1916), the Battle of the Somme (1 July 1916 - 18 November 1916), with the Battle of Verdun alone costing around 1 million lives for both the French and the Germans, and the Third Battle of Ypres, also known as the Battle of Passchendaele (31 July 1917 - 10 November 1917). Another significant event was the Gallipoli Campaign (17 February 1915 - 9 January 1916). It was a battle fought between the British forces and the Ottoman Empire (modern-day Turkey). It ended in total disaster for the British and resulted in a retreat.

    World Wars Ypres (Passchendaele) before and after the battle StudySmarterFig. 5 - Ypres (Passchendaele) before (top) and after (bottom) the Third Battle of Ypres (Battle of Passchendaele)

    In the meantime, Germany was also waging war on the Eastern Front with Russia. However, when Tsar Nicholas II of Russia was forced to abdicate on 15 March 1917 in light of the Russian Revolution, the Romanov Dynasty was overthrown. This gave rise to the power of Vladimir Lenin and the Bolsheviks, with the former stopping Russia's involvement and participation in WWI.

    Russian Revolution

    Russia had been under Imperial rule for centuries. At the time of World War I, the Romanov dynasty was in power, but social unrest had been brewing for many years. In October 1917, under leftist revolutionary Vladimir Lenin's leadership, the Bolsheviks seized power and replaced tsarist rule with a communist government. Later on, the Bolsheviks became the Soviet Union's Communist Party.

    The US had remained on the sidelines at first. However, when German U-boats sunk several commercial and passenger vessels that included US ships, on 6 April 1917, the US declared war on Germany.

    Germany decided to conduct warfare on two fronts based on the so-called Schlieffen Plan, a strategy devised about a decade earlier by Alfred von Schlieffen, a German Field Marshal. The flaw in the plan, however, was that it presumed an 'everything goes right' scenario, not taking into account any contingencies for things going wrong. In the end, this meant Germany's defeat.

    World Wars Alfred von Schlieffen StudySmarterFig. 6 - Alfred von Schlieffen

    The Second Battle of the Marne (15 July - 18 July 1918) was the beginning of the end, turning the tide to favour the Allied forces. On 11 November 1917, Germany signed an armistice agreement with the Allied forces, ending the fighting. Then, on 28 June 1919, exactly five years after Franz Ferdinand's assassination, which sparked the start of WWI, The Treaty of Versailles was signed. This was WWI's most crucial peace treaty, officially ending the world war.

    Military Technology

    New technological and scientific advances gave troops the tools to cause destruction on a massive scale. Some technological advances include heavy artillery, tanks, high explosives, machine guns, and tanks.

    A horrific scientific discovery introduced by the Germans in 1917 was mustard gas, which killed thousands of people by blistering the skin, eyes, and lungs.

    Did you know: WWI left about 20 million people dead, civilians and military personnel alike, and around 21 million injured?

    World Wars Europe in 1923, showing changes after WWI StudySmarterFig. 7 - Europe in 1923, showing changes after WWI

    World War 2

    Even though WWI ended in 1919, it was not the end of the instability in Europe. Adolf Hitler became Chancellor of Germany on 30 January 1933, taking power with his Nazi Party, which was the beginning of the destruction caused by WWII. Hitler anointed himself Führer and started to act on his obsession for the superiority of the so-called 'Aryan race', a pure German race.

    Aryan Race

    Hitler believed in an Aryan race, a pure German race. These were people whose blood (which he believed held a person's soul) was of the highest degree—a race created by God. Anyone who was not Aryan, such as Jews and Slavs, was considered inferior. These were dubbed 'Untermensch' (English: sub-human).

    Hitler signed alliances with Italy and Japan against the Soviet Union and rearmed Germany, the latter directly violating the Treaty of Versailles. Probably learning (somewhat) from Germany's mistake during WWI, Hitler did not want to fight on two fronts. On 23 August 1939, Hitler and Joseph Stalin signed the German-Soviet Nonaggression Pact. The pact promised no military action would be taken against the other for ten years. This left Hitler to carry out a long-desired plan: invade Poland, which he did on 1 September 1939. Two days later, Britain and France declared war on Germany, marking the beginning of WWII, a war between the Allied and Axis Powers.

    World Wars Joseph Stalin, 1920 StudySmarterFig. 8 - Joseph Stalin, 1920

    On 7 September 1940, the Germans started the Blitz, where Germany launched air attacks, bombing industrial targets, towns, and cities in the UK. The Battle of Britain was nearing its end, and the German Luftwaffe and British RAF fought it out in the air with a British victory, ending the Blitz on 11 May 1941.

    World Wars London, including St. Paul's Cathedral, after the Blitz StudySmarterFig. 9 - London, including St. Paul's Cathedral, after the Blitz

    In the meantime, Hitler wanted to expand Germany's territory, so he took two courses of action:

    1. The extermination of Jews throughout German-occupied Europe. This genocide became known as the Holocaust.
    2. Hitler went against the treaty he signed with Stalin and, under the code name Operation Barbarossa, ordered the invasion of the Soviet Union on 22 June 1941.

    The Holocaust

    The Jews did not fit Hitler's vision of the Aryan race, and he deemed them inferior. In 1941, plans for the 'Endlösung' (English: The Final Solution) were already introduced, and Jews across German-occupied Europe were sent to concentration camps such as Auschwitz-Birkenau. Many died, were killed in the streets, or died from hunger or weather conditions. Around 6 million Jews lost their lives, the vast majority in concentration camps.

    On 7 December 1941, Japan, Germany's ally, attacked and bombed Pearl Harbor in Hawaii, causing the US to declare war on Japan, officially entering WWII. Japan had several victories over the US before the US Pacific Fleet won the Battle of Midway on 6 June 1942.

    In North Africa, American and British forces won a victory over the Germans and Italians, causing Mussolini's government to fall in July 1943. In the meantime, Germany's counteroffensive on the Eastern Front was not going as planned, ending in the exceptionally bloody Battle of Stalingrad (23 August 1942 - 2 February 1943).

    On 6 June 1944, Operation Overlord launched D-Day, a massive seaborne invasion landing on the beaches of Normandy (France). The Battle of the Bulge started in December 1944 and was Germany's last major offensive. Things were not going well for Germany, and Hitler took his own life in his bunker on 30 April 1945.

    World Wars Allied forces land on Omaha Beach, Normandy on D-Day StudySmarterFig. 10 - Men of the 16th Infantry Regiment, US 1st Infantry Division landing on Omaha Beach, Normandy, on the morning of 6 June 1944, known as D-Day

    The campaigns at Iwo Jima (February 1945) and Okinawa (April-June 1945) cost many lives. Eventually, the US dropped two atomic bombs, one on Hiroshima and one on Nagasaki. World War II officially ended on 2 September 1945.

    Did you know: WWII was the deadliest international conflict in recorded history? While there are no exact numbers, an estimated 60 to 80 million people perished! Millions were injured, and even more people lost their homes, belongings, and properties.

    World Wars World War II deaths for Allied Forces and Axis StudySmarterFig. 11 - World II deaths for Allied Forces and Axis Powers

    In the aftermath, communism spread from the Soviet Union into eastern Europe. Soon the Soviet Union would stand off with the US in a conflict known as the Cold War.

    To end on a more positive note:

    • The 1945 Allied Conference in San Francisco (25 April 1945 - 26 June 1945) resulted in the creation of the United Nations (UN).
    • The Treaty of Maastricht created the European Union (EU) to bring back stability, peace, and prosperity to Europe. It was signed on 7 February 1992 and became effective on 1 November 1993.

    If you want to learn more, start with our article on the First World War, the origins of WWII, and the outbreak of WWII.

    World Wars - Key takeaways

    • A world war is a war where the world's superpowers are at war or at least involved in some capacity. This is different from a (civil) war, when war is between countries that are not considered superpowers, within a country, or between states or ethnicities.

    • World War I and World War II are the main wars we classify as world wars.

    • World War I's main catalyst was the assassination of Archduke Franz Ferdinand on 28 June 1914. A month later, on 28 July, Austria-Hungary attacked Serbia, marking the beginning of WWI.

    • Germany's decision to fight on two fronts, the Western and Eastern Front, is what eventually caused Germany to lose the war.

      • WWI officially ended on 28 June 1919 with the signing of the Treaty of Versailles.

    • World War II started on 3 September 1939, when Britain and France declared war on Germany after the latter invaded Poland two days earlier. It ended on 2 September 1945.

      • The most infamous part of WWII was the genocide of the Jews, known as the Holocaust.


    1. F.R. Shapiro. The Yale Book of Quotations. Yale University Press 2006
    2. The Culture of Einstein. NBC News (
    3. Fig. 6 - Alfred von Schlieffen ( by Lwc 21 (no profile) Licensed by CC BY-SA 4.0 (
    4. Fig. 7 - Europe in 1923 ( by Fluteflute ( Licensed by CC BY-SA 2.5 (
    5. Fig. 11 - World War II deaths ( by Piotrus (no profile) Licensed by CC BY-SA 3.0 (
    Frequently Asked Questions about World Wars

    What describes a World War?

    A world war is where the world's major superpowers are at war or are at least involved in some capacity. 

    What's the difference between a war and a world war?

    A world war is fought between the world's major superpowers, or at least are involved. A (civil) war is between countries that are not considered superpowers; it is a war within a country or between states and ethnicities. It is on a less global scale than a world war.

    When was World War 2?

    World War 2 started on 3 September 1939 when France and Britain declared war on Germany after Germany invaded Poland on 1 September. It ended on 2 September 1945.

    When was the First World War?

    The First World War started on 28 July 1914, with the war declaration of Austria-Hungary on Serbia, and lasted until 28 June 1919 with the signing of the Treaty of Versailles. 

    Who started the First World War?

    The First World War was started by Austria-Hungary when they declared war on Serbia. This was in retaliation for the assassination of Archduke Franz Ferdinand by a Serbian nationalist.

    Test your knowledge with multiple choice flashcards

    Germans sank over 200 American vessels off the coast of ______.

    Who was the Zimmermann Telegram addressed to?

    Who got Batum as a result of the Treaty of Brest-Litovsk?


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