What Were the Main Causes of World War I?

World War I began in August 1914 and ended with an armistice on November 11, 1918. The so-called “Great War” involved all the major powers of Europe, and for the first time in its history, the United States intervened in a foreign war and tipped the balance in favor of its allies, France and England.

Before the bloody trench war ended, more than 9 million men would die. Property loss and damage would total a staggering over $337 billion in direct and indirect costs – more than any war in the history of the world.

When it ended, the allied victors imposed a burden of reparations and other penalties on the Germans that would actively sow the seeds for the next and even more terrible World War.

What was the cause of all that waste and devastation? What were the causes of World War I?

Table of Contents

What caused World War I

Russia and Serbia

Mutual Defense Alliances

An intricate web of defense alliances meant that when one was threatened, the other(s) was obligated to help. Some major treaties were between the following European countries:

  • Russia and Serbia
  • Germany and Austria Hungary
  • France and Russia
  • Britain and France and Belgium


Rivalries for colonies in Asia and Africa among European powers led to an increase in tensions and confrontation that pushed the world into global war.


Arms races in the early 20th century resulted in a military buildup in Germany, Russia, and the naval forces of Great Britain.

The military establishment exerted greater influence on policy – especially in Germany.



The tinder box of World War I was the desire of Bosnia and Herzegovina to join Serbia and gain independence from Austria-Hungary.

In the rest of the world, nationalism played a role in convincing the population to hate foreigners and to prove their power and dominance.

The assassination of Archduke Franz Ferdinand

Archduke Ferdinand was the heir to the throne of Austria-Hungary. On June 28, 1914, the Archduke and his wife were assassinated by a Serbian nationalist.

Enraged by the assassination, Austria-Hungary issued harsh ultimatums to the Serbian government and one month later declared war on Serbia.

Prelude to World War I: The Balkan Wars of 1912-1913

If World War I was an explosion, its spark was the Balkans. The Balkan Wars of 1912 and 1913 left festering and unresolved nationalistic and territorial grievances.

The 1912 conflict wrested the remaining Turkish European possessions from the Ottomans, and the 1913 war was a quarrel between the victors – Greece, Bulgaria, and Serbia – over the conquered territory.

Bulgaria was defeated and sought support from its stronger neighbor, Austria-Hungary. In turn, Austria-Hungary forced Serbia to give up some of Serbia’s Albanian conquests, which inflamed Serbian resentment and was at the root of the Archduke’s assassination.

A timeline of events that plunged Europe into a 4-year war

Austria war on Serbia
  • July 28, 1914 – Austria declared war on Serbia.
  • August 1, 1914 – As Austria’s ally, Germany declared war on Russia, an ally of Serbia.
  • August 3, 1914 – Germany declared war on France, an ally of Russia, and immediately began an invasion of neutral Belgium after France declined to declare its neutrality in the conflict.
  • August 4, 1914 – Great Britain, an ally of France, declared war against Germany.
  • April 6, 1917 – The United States (President Wilson), after initially declaring that the country would remain neutral, declared war on Germany. The cause: unrestricted German submarine warfare and the infamous Zimmerman Telegram (see below).

The German Kaiser’s role in starting World War I

Soon, the world witnessed the spectacle of everyone declaring war on everyone else. Germany’s march through Belgium, a catalyst that brought Great Britain into the fray, was another indication that, whatever the excuse, Kaiser Wilhelm (who, by the way, was a grandson of England’s Queen Victoria) had imperial designs on his neighbors.

It is likely that if the Archduke’s assassination could have been prevented, Germany would have found another excuse to go to war, probably in some colonial territory in Africa.

The Germans harbored deep resentment and jealousy, having not been cut in completely on Europe’s colonization of the vast African continent the century before.

The Germans also might have been able to prevent the entry of the United States into the European land war.

Kaiser Wilhelm

However, Germany committed some strategic blunders that caused American public opinion to turn against Germany:

  • German unrestricted submarine warfare, resulting in American deaths at sea
  • The Zimmerman Telegram (see below)

Could the Germans have avoided these blunders? Probably, but that would have been out of character and not consistent with what the Kaiser felt was in German interests – especially his willingness to sink ships carrying supplies and weapons of war that could be used against Germany.

The tremendous arms and naval buildup in Germany during the years before the war, as well as German resentment over being left out of the race for colonies, pushed the Kaiser and his military establishment headlong into war.

The Kaiser and his advisors hoped for a quick victory and a knock-out of the French and British. What they got instead was protracted and bloody trench warfare.

Trench warfare on the European Western Front

World War I witnessed trench warfare at an unprecedented level. Armies of millions of bedraggled and flea-bitten soldiers faced each other in parallel lines of trenches that extended from the coast of Belgium in the north through northeastern France down to Switzerland.

Trench Warfare

The trenches became a necessity during the first few months of the war. Great offensives launched by Germany and France failed against withering machine-gun fire and rapid-firing artillery.

The overwhelming firepower and sheer quantity of shells and bullets flying through the air meant that soldiers had to dig into trenches to survive.

Opposing armies on the Western Front continuously tried to break through each side’s trench system with infantry assaults – and those attacks usually failed.

What was needed for a breakthrough was surprise and overwhelming numbers. What turned the tide was America’s entry on the side of England and France.

What brought America into World War I

Two years into the War, the conflict spread to the Western Hemisphere when the United States entered on the side of the Allies.

President Woodrow Wilson tried to maintain American neutrality during the first years of the war.

He even won reelection on the slogan, “He kept us out of war.”

Wilson correctly perceived that there was no great support on the part of the American public for involvement in a foreign war.

Even the early loss of American lives on the high seas as a result of German submarine warfare wasn’t sufficient to tip the balance in favor of war.

Everything changed with the publication of the infamous Zimmerman Telegram to the Mexican government.

The German Foreign Minister sent a coded telegram to his ambassador in Mexico.

Brought America

The British Admiralty Intelligence intercepted the telegram. It was published in the U.S. press and immediately set off a nationwide demand for war against Germany.

In the telegram, the Germans told the Mexican government that, if the United States should enter the war against Germany, Mexico should become Germany’s ally.

Mexico’s reward if Germany won would be recovering Texas, New Mexico, and Arizona from the United States.

This incident and the German announcement of the resumption of open submarine warfare led Wilson to ask Congress to declare war on the Germans.

In the end, America’s entry into the war in Europe tipped the balance for the allies. An exhausted and defeated Germany sued for peace and signed on June 28, 1919, exactly five years after the Archduke’s assassination.

How World War I changed Europe and the United States

At the end of World War I, the political and cultural face of Europe was altered drastically. The royal dynasties of Germany and Russia were toppled by revolution.

In their place, the Germans endured almost 20 years of social and economic devastation leading to the rise of Hitler; the Russians experienced a period of internal strife and civil war as the Communists consolidated their power.

Inevitably, territorial readjustments occurred as disputed territory changed hands. New political entities Yugoslavia, Austria, Hungary, Syria, and Russian border countries of Estonia, Lithuania, and Latvia emerged.

World War I Changed Europe

France once again assumed custody of the Alsace Lorraine. Also, Germany lost overseas colonial possessions and the borders of Poland were again redefined.

The United States emerged from the war as a power of both industry and war. As such, Woodrow Wilson hoped to accomplish lofty goals of the successful completion of a “war to end wars,” making the world “safe for democracy,” which would be embodied in the establishment of the League of Nations.

President Wilson’s aims were thwarted by a postwar resurgence of American isolation and a spirit of revenge and vindictiveness on the part of his victorious European allies.

Without American membership, the League of Nations proved to be ineffective and was unable to do much to forestall World War II.

The Treaty of Versailles imposed crippling sanctions that plunged a defeated Germany into bankruptcy and into the arms of Adolf Hitler and his Nazi regime.

The vanquished Germans had absolutely no say in the treaty’s harsh provisions. The Allies did not consult with German leaders, who didn’t see the treaty until just weeks before they were ordered to sign – or face an allied invasion.

Besides the loss of territory, the treaty imposed harsh financial penalties. The treaty appeared to have one major purpose: to bankrupt Germany and prevent any chance of economic recovery because of excessive war reparations.

Germany was required to pay the allies over $15 billion, an amount Germany could not pay.

These reparations ruined Germany financially and set the stage for the rise of the ultra-nationalist Nazis.

It was World War, Part 1


It could be argued that our world really experienced only one war. It was the war that began in 1914 and annihilated one full generation of young men.

When they ran out of cannon fodder temporarily, our leaders imposed a pause to allow the world to forget the carnage and horror.

The war recommenced in 1939 after Hitler denounced the Treaty of Versailles as a document signed by traitors to the fatherland.

So, countries that went to war again learned little from World War I, except that they had mostly the same reasons for fighting.

Yes, World War I was inevitable. Tragically, so was World War II. As the vengeful, short-sighted policies of England and France imposed crippling penalties and humiliation on Germany, yet another generation of young men grew up to lie beneath the row-on-row of white cemetery crosses.