Competition: the competition for colonies was another source of international antagonism. The great powers sectioned off Africa among them, established spheres of influence in China and sought protectorates elsewhere. Sooner or later this rush to appropriate new territories was destined to spark disagreements over boundaries of control.
Militarism: all the countries within the hostile camps were building large armies and navies during the pre-war years. As a result, a class of professional and powerful military officers developed and they tended to dominate the civil authorities. In addition, before the conflict happened, the militaries of each country had drawn up complete plans for mobilization. These plans only awaited the go-ahead signal. The existence of secret battle plans stimulated the practice of spying, which in turn aroused greater hatred and fear.
Nationalistic Beliefs: strong feelings of nationalism fed the fires of hatred in pre-war Europe. It turned Frenchman against German and Russian against Austrian. Nationalistic speeches and writings hastened the war by portraying it as the best test for proof of national superiority.
The immediate cause of the war was the assassination of Archduke Francis Ferdinand, the heir to the throne of Austria-Hungary, by a Serbian nationalist. On the morning of June 28, 1914, while traveling in a motorcade through Sarajevo, the capital city of Bosnia and Herzegovina, Archduke Francis Ferdinand and his wife Sophie were assassinated by a Serbian nationalist. The Archduke had ignored warnings of a possible assassination plot and decided to tour the capital on the anniversary of the 1389 battle of Kosovo. In this battle the Turks, ending Serbia’s independence as a nation, defeated Serbia.
The Archduke was chosen as a target because Serbians were afraid that after his ascension to the throne, he would continue the persecution of Serbs living within the Austro-Hungarian Empire. Serbia had gained independence from the Ottoman Empire in 1878. At that time, Serbia laid claim to several regions of Bosnia and Herzegovina, which were inhabited primarily by Serbs. However, the Congress of Berlin granted permission to Austria-Hungary to occupy Bosnia and Herzegovina, including the disputed Serbian areas. In 1908, Austria-Hungary officially annexed all of occupied Bosnia and Herzegovina, adding additional fuel to the fires of Serbian nationalism.
As Francis Ferdinand and his party proceeded through Sarajevo, the first of the Black Hand, a secret terrorist organisation, operatives tossed a bomb at the Archduke's automobile. The chauffeur saw the explosive and accelerated to avoid the impact. Sophie ducked, and Francis Ferdinand deflected the bomb with his arm, causing it to bounce off the back of the car and explode behind them, destroying the car following behind and seriously injuring several aides. To avoid arrest and questioning, the unsuccessful assassin, nineteen-year-old Nedjelko Cabrinovic, swallowed a cyanide pill and jumped into the river. However, he was hauled out of the river and detained.
As the Archduke's entourage resumed its tour of Sarajevo, the Archduke's chauffeur took a wrong turn and drove within ten feet of another Black Hand agent, Gavrilo Princip. Princip stepped up to the car and fired two pistol shots. One bullet hit Sophie, killing her instantly. The other hit Francis Ferdinand, who died within minutes. Like Carbinovic, Princip attempted suicide, but was captured before succeeding.
Austrian reaction to the assassination was swift, as the Sarajevo crisis was seen as the Empire's last chance to assert its supremacy in the Balkans. Austrian foreign minister Count Leopold von Berchtold was determined to make use of the assassinations to crush once and for all the Serbian nationalist movement. Berchtold sent an envoy to Berlin, who was assured by Emperor William II on July 5th that Germany would fully support any action which the Dual Monarchy might take against Serbia. On July 6th, German chancellor Theobald von Bethmann-Hollweg issued the blank check of unconditional German support.
On July 23, 1914, Austria-Hungary presented Serbia with a lengthy list of demands, with a 48- hour period in which to comply. These demands included abolishing all Pan-Serb propaganda, expelling from office any persons thought to have nationalist sympathies, taking legal action against certain officials designated by Austria-Hungary, and allowing agents of the Dual Monarchy to control all investigations and proceedings concerning the Sarajevo murders. Minutes before the July 25th deadline, Serbia issued a conciliatory reply to Berchtold's demands, stating that Serbia wished the dispute to be submitted to the International Tribunal at the Hague. This conciliation was rejected. On July 28, 1914, Austria-Hungary declared war on Serbia. World War I had begun.