The first declaration of war in World War I was made by Austria-Hungary. On July 28, 1914, Austria-Hungary declared war on Serbia. The immediate cause for this declaration was the assassination of Archduke Franz Ferdinand, the heir to the Austro-Hungarian throne, by a Serbian nationalist on June 28, 1914, in Sarajevo, Bosnia.

The assassination of Archduke Franz Ferdinand served as a catalyst for the tensions that had been brewing in the region. Austria-Hungary saw the assassination as an act of aggression and an opportunity to assert its authority over Serbia. In its declaration of war, Austria-Hungary presented a list of demands to Serbia, which included the suppression of anti-Austrian groups and allowing Austrian authorities to investigate the assassination.

However, the underlying causes for Austria-Hungary’s decision to declare war on Serbia were rooted in complex political and nationalist dynamics. Austria-Hungary aimed to maintain its influence in the Balkans and prevent the rise of Serbian nationalism, which posed a threat to its multi-ethnic empire. The Austro-Hungarian government also had the backing of its ally, Germany, which encouraged and supported its actions.

As for the Ottoman Empire, its entry into World War I occurred on the side of the Central Powers (Germany, Austria-Hungary, and Italy). The Ottoman Empire’s decision to join the war was primarily driven by strategic interests and a desire to reclaim lost territories.

The Ottoman Empire had been experiencing a period of decline and territorial losses prior to the war. It sought to regain control over territories in the Balkans and the Middle East. The empire’s leaders, known as the Young Turks, saw an opportunity to strengthen their position by aligning with the Central Powers.

In October 1914, the Ottoman Empire entered the war by launching an attack on Russian ports in the Black Sea. The empire’s entry into the conflict brought the war to the Middle East and resulted in the famous Gallipoli Campaign, where Allied forces attempted to secure control of the Dardanelles Strait and gain access to Constantinople (now Istanbul).

The Ottoman Empire’s involvement in the war had significant consequences, including the Armenian Genocide, the reshaping of borders in the Middle East through the Sykes-Picot Agreement, and the eventual collapse of the empire itself.

In summary, Austria-Hungary made the first declaration of war in World War I due to the assassination of Archduke Franz Ferdinand and its desire to assert control over Serbia. The Ottoman Empire joined the war to pursue its own strategic interests and reclaim lost territories.