Final answer:
Austria-Hungary was part of the Triple Alliance with Germany and Italy, but after the assassination that led to WWI, Germany was the main ally that provided unconditional support, leading to a complex web of alliances being activated.
Step-by-step explanation:
Austria-Hungary had a treaty with Germany, which is often referred to as the blank check assurance. Germany offered unconditional support to Austria-Hungary, which eventually led to a declaration of war on Serbia on July 28, 1914, after the assassination of Archduke Franz Ferdinand. This sparked a series of events that saw the activation of various alliances, pulling major powers into World War I. The Triple Alliance originally included Germany, Austria-Hungary, and Italy, while the Triple Entente comprised Britain, France, and Russia. Despite the Italian alliance, Italy initially remained neutral and later joined the opposing Allied Powers. Germany's invasion of Belgium brought Britain into the war, and the entry of the Ottoman Empire on the side of the Central Powers further expanded the conflict.