Germany's allies during World War I were Austria-Hungary, the Ottoman Empire, and Bulgaria. These formed the Central Powers and were opposed by the Allies, or the Entente, composed principally of Great Britain, France, the Russian Empire, and (later) the United States.

Though the evaluation of World War I as an imperialist war can be criticized as simplistic, I believe it is the best way of understanding what the war was really about and the deeper causes of it. The immediate cause of hostilities was the assassination of the Archduke Franz Ferdinand, the heir to the Austro-Hungarian throne, by a Serbian nationalist in June of 1914 in Sarajevo, Bosnia-Herzegovina, which at that time was a territory of Austria-Hungary.

Serbian nationalists, allegedly backed by Russia as part of a pan-Slavic movement, regarded Bosnia as part of their homeland and wished to free it from Austrian control. The belief on the part of the Austrians that Russia was behind the assassination led to a declaration of war. Alliances were already in place, meaning treaties had been signed in which each country had agreed to support its fellow signatories in case of war. Given that Germany was an official ally of Austria-Hungary, Germany thus declared war on Russia as well, and France and Britain, being allies with Russia, entered the conflict on the Russian side against Austria-Hungary and Germany.

For those not familiar with the system of alliances that had dictated the conduct of European (and other) countries for centuries, all of this may sound contrived and artificial. The question that must be asked is always "Why were such binding alliances formed in the first place?" What did the signatories to such treaties have to gain by signing them and by becoming involved in large-scale wars when there was ostensibly no direct threat to their own countries?

The answer is basically that at this point, 1914, the major European states were all involved in massive competition for power and resources. Germany had become a unified nation-state only forty-three years earlier. For centuries, Germany had been a patchwork of small, independent states loosely unified by a kind of quasi-mythic concept of ethnic solidarity known as the Holy Roman Empire. When these states (apart from Austria, which retained its separateness as co-leader of its own multiethnic empire) were unified, the balance of power in Europe was altered. Britain and France saw a new danger in a powerful state in the center of Europe that was prepared to compete with them for colonies and resources outside of Europe as well as to influence and control the smaller, less powerful European countries.

In addition, Britain, France, and Russia had long had their hands in the weakening Ottoman Empire, the so-called "sick man of Europe." Germany, however, had recently formed an alliance with the Ottomans, essentially displacing Britain as the principal European power making a client-state of the Ottoman Empire. In addition, the German-Ottoman alliance threatened Russian dominance in Central Asia and the all-important trade routes to Asia, including, of course, the recently completed Suez Canal. These routes were crucial to the British, French, and Dutch imperialist systems. Therefore Britain, France (which had been defeated in the Franco-Prussian War in 1870 and was itching for revenge against the Germans), and Russia had made common cause against Germany. Germany, in ethnic solidarity with Austria (threatened, as it felt itself, by the assassination of its heir at the hands of a Russian-allied national movement), was ready to get its licks in, to put it colloquially, against the British, French, and Russians.

Germany felt it had centuries of catching up to do in order to bring itself to the same power level as other countries, which had already been unified nation-states for hundreds of years. The Germans believed—to some extent, correctly—that the other powers had always wanted the German-speaking peoples to remain fragmented and disunited. Germany also wanted to manipulate the moribund Ottoman Empire, completing its plans for a Berlin-to-Baghdad railway and cynically taking advantage of nationalist Turkish sentiments to establish its own colonial control over much of the non-Turkish territory of that Empire. All of these were factors that led to Germany's entry into the war and the tragic and horrific events of 1914 to 1918.

Germany was not the instigator of World War I, but it was a key player in the war.  Germany signed a treaty with Austria-Hungary promising support if the nation was threatened.  After the assassination of the Austrian Archduke Franz Ferdinand by Serb nationalist Gavrilo Princip, Austria-Hungary gave Serbia a list of unreasonable demands to meet or else it would be invaded.  Serbia, a Slavic nation, appealed to Russia, as Czar Nicholas II claimed to defend all of the Slavs.  Russia started to mobilize in an attempt to intimidate Austria-Hungary into backing down. Austria-Hungary secured German backing for its own mobilization.  Germany feared Russian mobilization as well and it declared war on Russia.  France, bound by treaty to defend Russia, then entered the war against Germany.  

The Central Powers included Germany, Austria-Hungary, the Ottoman Empire, Italy, and Bulgaria.  The Ottoman Empire was in this coalition because it was angry at Russia after the Balkan Wars and wanted to regain territory lost.  Germany also hoped that the Ottoman Empire would threaten British interests.  Italy, a charter member of the Central Powers, would switch sides because it coveted Austro-Hungarian land.  

World War I was precipitated by the assassination of Archduke Franz Ferdinand, heir to the throne of Austria-Hungary, in Sarajevo on June 28, 1914. A Serbian nationalist named Gavrilo Princip shot the archduke, and this action caused Austria-Hungary to declare war on Serbia on July 28, 1914. Then, a series of countries were dragged into the war because of their alliances. Russia began to prepare for war, and, after delivering an ultimatum to Russia to stop its mobilization for war (Russia refused), Germany declared war on Russia on August 1. Germany became entangled in the war because it was the ally of the Austro-Hungarian Empire. The Central Powers went on to include not only Germany and Austria-Hungary, but also the Ottoman Empire and Bulgaria. On the opposing side, the Allied Powers included France, Great Britain, Russia, Serbia, and other countries, including, eventually, the United States. 

There are several reasons why Germany was involved in World War I. Germany became a unified country in 1870. By this time, most of the lands that were available for colonization were already controlled by other imperial powers. Thus, for Germany to get colonies, they were going to have to most likely fight to get these lands.

Knowing going to war was likely to occur, Germany began to build up its military. This alarmed other European countries that also began to build up their military. Germany built its military with the intent to put it into action. Germany wanted to be a world power and knew fighting would likely occur.

Germany had an alliance before World War I began. This was known as the Triple Alliance. It included Germany, Austria-Hungary, and Italy. When World War I began, Germany had an alliance called the Central Powers. This alliance included Germany, Austria-Hungary, Turkey, and Bulgaria. Italy fought on the side of Great Britain, France, and the Soviet Union in World War I. Since Austria-Hungary asked Germany to support its upcoming declaration of war on Serbia, Germany felt obligated to honor its alliance with Austria-Hungary. Thus, Germany agreed to support Austria-Hungary if they declared war on Serbia. Germany also believed it might be able to accomplish some of its goals if Austria-Hungary was successful with its attack on Serbia and the Balkan region.

The start of World War I was partially an attempt by Germany and other countries to achieve various goals they had in terms of achieving the status of becoming a world power. This war, and later World War II, was Germany’s attempt to gain land, power, money, and influence.