World War I was undoubtedly one of the most devastating and widespread conflicts in the history of mankind, opening the theater of war across continents and breaking a delicate balance of power that had been in place for centuries. In order to find out exactly what caused the First World War, it is necessary to look back at the factors that led to the animosity between Germany, France, Russia, Britain, and Austria-Hungary, among others (some of these conflicts simmering for at least forty years leading up to the war). It was a complex, interweaving and stacking series of events that eventually brought the entirety of Europe, as well as America, into a tense, years-long and costly conflict that changed the face of war forever.
Understanding the various political factors of World War I's major players leading up to the war gives incredible insight into the reasons why these nations went to war. In the 1912 German election, the nation elected many different left-wing parties, such as the SPD (Social Democratic Party of Germany); this frightened and worried the Prussian Junkers, who wanted to curb the fervor that was rising for these parties. This might have contributed to the entrance of Germany into the war, as the reigning powers wanted a distraction from the rise of these left-wing parties.
Austria-Hungary was the country where most of the groundwork was laid for the First World War; the feudal nature of the country was starting to ebb, as the German aristocracy was losing power over the country in the wake of a new wave of nationalism. With the establishment of the Ausgleich, and the reestablishment of the German aristocracy to greater power, the rest of the country felt disenfranchised and dissatisfied with the direction their country was headed in. To that end, war with Serbia started to become more and more of a concern, as Serbia itself became more and more of a military power. Their subsequent escalation of military forces in light of this threat is one major factor that contributed to the start of World War I.
The concept of imperialism played a heavy role in the start of World War I - due to the success of Great Britain and France in creating huge empires through trade control and foreign resources in the 19th century, many other countries in Europe attempted to repeat that success, to frustrated results. Because of the trade balance in place, there were only so many natural resources to go around in Europe, which stunted the potential of these other countries (like Germany, Austria-Hungary, Russia and others) to achieve their ambitions. On the part of the Russians, specifically, their primary goals included making sure they were protected from the expanding military of Turkey, which was being helped by German officers and technology. When they eventually joined World War I, their chief objectives included getting the Turks out of Constantinople, annexing Galicia and others; these goals would make sure that Russia was the most powerful force in the Black Sea.
One of the most important considerations to make in discerning the start of World War I is the nature of alliances in the early 20th century between European countries. In this time, there were many mutual defense agreements in place that brought many different countries at war with each other; this established a balance of power. In essence, if one ally went to war, the other countries provided support and joined their war effort. This was absolutely the case with Germany and Austria-Hungary, as well as Russia and Serbia, and a conjoining web of other alliances that involved France, Britain, Belgium and others. It was the dragging of these larger countries into the Austria-Hungary/Serbia conflict that made this international spat into a large world war.
There was also an Anglo-German naval arms race that helped to escalate the military might of both countries, and made them more prepared for war. Germany expanded their navy dramatically, which then led Britain to expand their Royal Navy to a great extent in order to keep up with the threat. Though the Germans eventually stopped building up their navy, it was one of the reasons Britain joined the Triple Entente, thus ensuring the building of the alliance system that escalated the Austria-Serbian conflict into a world war. Furthermore, it had established Germany as a great and powerful world military power, which would cement its status as one of the bigger military forces to participate in the war. This arms race helped to create the weapons that facilitated the war itself.
The Franco-Prussian War, which lasted from 1870 to 1871, can be seen has building the inroads for many of the conflicts that caused World War I. At the end of the war, Germany was more powerful than ever; this started to upset the balance of power in Europe, as Germany became much more militarily strong than the rest of Europe was comfortable with or prepared for. German nationalism was at an all-time high, and its economy was extremely strong. Because of this, Germany and France began to build a long history of animosity, particularly due to the Germans annexing Alsace-Lorraine from the French. As a result, the French had a strong desire to enact revenge on Germany for these slights; however, their defeat in the war made France politically unstable, which led to the creation of the French Third Republic. Because of these various factors, anti-German sentiment was rampant in France, despite their eventual recovery from their losses in the Franco-Prussian War.
Austria and Serbia already had substantial tensions existing between then by the time of the First World War. In 1903, Serbian officers assassinated King Alexander I, electing a new king in their place and taking more of their business from Austria-Hungary and toward France and Russia. Austria-Hungary, desperate to gain a more solid foothold in Bosnia-Herzegovina, annexed them in 1908, setting off the Bosnian Annexation Crisis, a series of protests and diplomatic hiccups that lasted more than a year, and was only solved with the Treaty of Berlin. While this smoothed things over, tensions between Austria-Hungary, Russia and Germany continued.
This tension was exacerbated with the Balkan Wars of 1912 and 1913, of which there were two. The results of these wars included another shift in the balance of power in Europe, which strongly favored Russia and Serbia. The First Balkan War came about after Serbia demanded a port in Albania, which the Austrians soundly refused, leading to military action. The Second Balkan War came about after a preemptive strike by Serbia and Greece against Bulgaria. After both wars were over, Germany and Austria-Hungary's alliance was shaken, as Germany was divided on the subject of their continued and costly obligation to support Austria-Hungary in its continual conflict with Serbia. The German Imperial War Council of 1812 eventually decided it could not support Austria-Hungary against Serbia and its allies any longer. This broke down foreign relations dramatically, and Germany continued to help Austria-Hungary less and less.
The first real shot of the First World War came with the assassination of Archduke Franz Ferdinand of the Austo-Hungarian Empire on June 28, 1914. As the presumptive heir to the throne of Austria-Hungary, he was assassinated by a group of Serbian assassins from Bosnia in Sarajevo. Due to this incredible and dramatic act of war, Austria-Hungary declared the July Ultimatum, which demanded that Serbia fulfill a series of demands within 48 hours, or it would recall the Serbian ambassador and declare war. Germany declared their support for Austria's position on the matter, and Serbia acquiesced to most of the demands, but hesitated on some that threatened their ability to survive as a nation. With that, as well as a few choice skirmishes along the Austrian-Serbian border, other nations around the world, including Russia, Italy, France and the United Kingdom began discussing measures to mobilize to support Austria as part of their alliances.
Austria-Hungary, with this decision made, chose to invade Serbia; the Russians, in turn, mobilized their forces against Austria-Hungary and their German allies. Because of France's alliance with Russia, the Germans mobilized and turned to invade France in July of 1914 to take out the French army, leaving it out of the way to eliminate Russia. Because of these mobilizations, and the invasion of Belgium by Germany, the United Kingdom and France declared war on Germany, while Germany declared war on Russia. With these declarations in place, the First World War had begun.
In conclusion, a great many things led to the First World War, all dealing with imperialism, nationalism, and the shaky balance of power that existed in Europe between nations. The mutual defense agreements that were in place between nations created larger conflicts out of smaller ones. Previous wars and conflicts shifted the balance of power between different nations, destabilizing the region further. Nationalism and imperialism caused nations to take greater steps toward dominance, ignoring the needs of other nations for the sake of conquering. The assassination of Archduke Franz Ferdinand sped along this process, leading to the invasion of Austria-Hungary into Serbia, and their various allies falling into place as per their alliances. Despite this singular event pushing the nations of Europe into war, it was absolutely the straw that broke the camel's back, as decades of animosity, army-building, imperialism and nationalism combined to create an environment that was conducive to world war. Germany and Austria-Hungary's push for control of Serbian interests, and their testing of other nation's treaties, undoubtedly led to the First World War.
Holger H. Herwig, The First World War (Bloomsbury USA, 2009).
Norman Stone, The Eastern Front (Penguin Global, 2004), 2nd ed.