The seeds of World War One began with territorial and economics rivalries that dated back to the 19th Century. One of the first hallmarks of WW1 was German Chancellor Von Bismarck's formation of the Triple Alliance (Germany, Austria/Hungary), as well as the Franco-Prussian War, where Prussia was deprived of Alsace Lorraine, with help from the North Germany Confederacy, ultimately becoming part of Germany. This was the beginning of a long anonymousity on France's part toward Germany.)

When German Emperor Wilhelm succeeded Von Bizmarck as ruler of Germany, the country began an expansionist militaristic policy. This, along with its alliances to Austria/Hungary--who had a new nationalist policy--made Germany a formidable presence in the region, which was a matter of concern to all of Europe. It was especially a threat to Great Britain's dominance as the great world power of the day.

The European powers had come into conflict over certain areas in China, Africa and the Middle East which were left wide open by the decline of the Ottoman Empire. (AKA, the Turkish Empire, which existed from 1299-1919) in a series of battles known as the Balkan Wars.

The Balkan Wars (1912-1913) were a collection of conflicts for possession of territories which formerly belonged to the Ottoman Empire. Among the several small wars, Italy and Serbia both fought Turkey over Tripoli in 1912, and in 1913 Serbia fought Bulgaria over Macedonia. Serbia, in particular, profited from these wars, in an attempt to regain its former glory as an empire.

Austria was very threatened by the idea of an increasingly powerful Serbia at its door. Also, Serbia had allied itself with Russia. The Russians were long time enemies of the Ottoman Empire and many in Europe feared Russia might make some aggressive moves now that the Ottoman Empire was on its last legs. The fact that Serbia was allied with Russia gave Austria an additional excuse to be hostile toward the Serbs. This caused Austria to induce its ally Germany to see Serbia as an enemy. Seeing as Germany was already intimidated by the idea of Russian expansion, they needed very little motivation to be hostile to any Russian ally.

Serbia supported the pro-Slavic separatist movement in Bosnia-Herzegovina, which was under Austro-Hungarian rule. The Serbs encouraged terrorists acts and political assassinations. A group called the Black Hand was formed in Bosnia, whose agenda was to strike against the Austrian occupation.

In June 1914, Austrian military Chief Inspector General Arch Duke Franz Ferdinand paid a visit to Sarajevo in Bosnia. He and his wife were assassinated by Black Hand members led by Gavrillo Princip, who performed the actual killings.

This led to an ultimatum by the furious Austrians. They demanded...An official apology from Serbia; a promise that Serbia would denounce all acts of rebellion by Slavs against Austria; Cut all ties to groups like the Black Hand; Dissolve all periodicals that have written anything against the Austrian occupation; Stop the teachings or public speaking by anyone anti-Austrian; Agree to arrest anyone from a group that demonstrates against the Austrians; And to arrest any public officials who have supported Bosnian independence. Serbia, backed by their Russian allies, refused to meet these demands.

Austria, who had been looking for a reason to fight the Serbian, used this as an excuse to go to war, backed by their ally Germany. Russian mobilization in support of Serbia caused Germany to declare war on Russia. The remnants of the Ottoman Empire joined Germany and Austria in opposition of their old nemesis the Russians.

France, who had long resented Germany, gave vocal and financial support to Serbia and Russia. Old grudges led an overly aggressive Germany to impulsively declare war on France as well.

Great Britain had long seen Germany as the greatest threat to their position of power in the world. When Germany sent troops through Belgium, the British used this as a reason to declare war on the Germans.

A domino effect began with other countries taking sides due to their political position at the time and the scope of the conflict increasing exponentially.

Japan reluctantly joined the war on the side of Britain and France. They saw the Russians and Germans as a greater threat to their region of the world than the British and their allies, and so eneded up helping the British fleet repel their enemies in the Pacific.

After the sinking of the Lusitania in 1915, as well as reports of other German attacks on civilian ships in the Atlantic, the United States joined the War in April 1917. The war was already well under way by then.