The causes of World War I, also known as the Great War, have been debated since it ended. Officially, Germany shouldered much of the blame for the conflict, which caused four years of unprecedented slaughter. But a series of complicated factors caused the war, including a brutal assassination that propelled Europe into the greatest conflict the continent had ever known.

In June 1914, Austrian Archduke Franz Ferdinand and his wife Sophie traveled to Bosnia—which had been annexed by Austria-Hungary—for a state visit.

On June 28, the couple went to the capital city of Sarajevo to inspect the imperial troops stationed there. As they headed toward their destination, they narrowly escaped death when Serbian terrorists threw a bomb at their open-topped car.

Their luck ran out later that day, however, when their driver inadvertently drove them past 19-year-old Serbian nationalist Gavrilo Princip who shot and killed Franz Ferdinand and his wife at point-blank range. Austria-Hungary was furious and, with Germany’s support, declared war on Serbia on July 28.

Within days, Germany declared war on Russia—Serbia’s ally—and invaded France via Belgium, which then caused Britain to declare war on Germany.

A state’s desire to expand its empire was nothing new in European history, but by the early 20th century the Industrial Revolution was in full force.

New industrial and manufacturing technologies created the need to dominate new territories and their natural resources, including oil, rubber, coal, iron and other raw materials.

With the British Empire extending to five continents and France controlling many African colonies, Germany wanted a larger slice of the territorial pie. As countries vied for position, tensions rose, and they formed alliances to position themselves for European dominance.

During the 19th century, rising nationalism swept through Europe. As people took more pride in their country and culture, their desire to rid themselves of imperial rule increased. In some cases, however, imperialism fed nationalism as some groups claimed superiority over others.

This widespread nationalism is thought to be a general cause of World War I. For instance, after Germany dominated France in the Franco-Prussian War of 1870-71, France lost money and land to Germany, which then fueled French nationalism and a desire for revenge.

Nationalism played a specific role in World War I when Archduke Ferdinand and his wife were assassinated by Princip, a member of a Serbian nationalist terrorist group fighting against Austria-Hungary’s rule over Bosnia.

In 1879, Germany and Austria-Hungary allied against Russia. In 1882, Italy joined their alliance (The Triple Alliance) and Russia responded in 1894 by allying with France.

In 1907, Great Britain, Russia and France formed the Triple Entente to protect themselves against Germany’s growing threat. Soon, Europe was divided into two groups: The Central Powers of Germany, Austria-Hungary and Italy; and the Allies, which included Russia, France and Britain.

As war was declared, the allied countries emboldened each other to enter the fray and defend their treaties, although not every coalition was set in stone—Italy later changed sides. By the end of August 1914, the so-called “entangled alliances” had caused what should have been a regional conflict to expand to all of Europe’s powerful states.

In the early 1900s, many European countries increased their military might and were ready and willing put it to use. Most of the European powers had a military draft system and were in an arms race, methodically increasing their war chests and fine-tuning their defense strategies.

Between 1910 and 1914, France, Russia, Britain and Germany significantly increased their defense budgets. But Germany was by far the most militaristic country in Europe at the time. By July 1914, it had increased its military budget by a massive 79 percent.

Germany was also in an unofficial war with Britain for naval superiority. They doubled their naval battle fleet as Britain’s Royal Navy produced the first Dreadnought battleship which could outgun and outrun any other battleship in existence. Not to be outdone, Germany built its own fleet of Dreadnoughts.

By the start of World War I, the European powers were not just prepared for war, they expected it and some even counted on it to increase their world standing.

Although the assassination of Archduke Ferdinand was the spark that caused Austria-Hungary to strike the first blow, all the European powers quickly fell in line to defend their alliances, preserve or expand their empires and display their military might and patriotism.