The passage can best be used to explain the role of which of the following in bringing about the first world war?

Question: The passage can best be used to explain the role of which of the following in bringing about the first world war?

The intricate web of alliances formed in the years leading up to World War I played a pivotal role in the outbreak of the conflict. The alliances, which were intended as deterrents against war, ironically became catalysts for it. The assassination of Archduke Franz Ferdinand of Austria-Hungary by a Serbian nationalist set off a chain reaction among the allied nations. Austria-Hungary's declaration of war on Serbia activated a series of mutual defense agreements, leading to the rapid involvement of all the major European powers. This included Germany and Austria-Hungary on one side, known as the Central Powers, and the Triple Entente—comprising Great Britain, France, and Russia—on the other. These alliances were formed over the previous decades, largely as a response to the shifting balance of power on the continent, particularly the rise of a unified Germany. The alliances were supposed to create a balance of power that would prevent any one nation from dominating Europe, but instead, they created a situation where a conflict between two countries could quickly escalate into a full-scale war.