Final answer:
The 'powder keg' that would explode into the First World War in 1914 was Nationalism in the Balkan countries and their strained relationship with Austria-Hungary.
Step-by-step explanation:
The 'powder keg' that would explode into the First World War in 1914 was Nationalism in the Balkan countries and their strained relationship with Austria-Hungary. The Balkan countries, such as Serbia, Bulgaria, and Greece, were seeking independence from the declining Ottoman Empire and had territorial disputes among themselves. These tensions were exacerbated by Austria-Hungary's desire to maintain control over the region, leading to a combustible situation.
This can be seen in the assassination of Archduke Franz Ferdinand of Austria-Hungary by a Bosnian Serb nationalist in 1914, which triggered a series of events that eventually led to the outbreak of the war. The assassination was fueled by nationalist aspirations for a greater Serbia, and Austria-Hungary's response to the assassination further escalated the tensions, eventually drawing other European powers into the conflict.
Learn more about Causes of the First World War