Final answer:
Tensions between European nations rose due to a combination of imperial rivalries, territorial disputes, nationalism, and alliances. The Franco-Prussian conflict over Alsace-Lorraine and competitive imperialism, especially between Germany and Great Britain, were central. Treaties forcing allies into conflict and the weakening Ottoman Empire also played significant roles.
Step-by-step explanation:
The rise in tensions between European nations was primarily caused by a complex mix of imperial rivalries, territorial conflicts, nationalism, and the formation of military alliances. The acquisition of Alsace-Lorraine by Prussia after defeating France and the subsequent arms buildup heightened frictions. Moreover, the advent of nationalism spurred revolts and agitation for independence within and across nations, as seen with the Irish against British rule and the assassination of the Austro-Hungarian archduke by Serb nationalists, sparking the onset of World War I.
Imperial ambitions and the struggle for colonial dominion further fueled disagreement among European powers. Germany's emergence as a unified nation and its subsequent quest for global recognition and colonial expansion directly challenged the established imperial powers like Great Britain. This competition inevitably led to military buildups and alliances that divided Europe into opposing camps, setting the stage for potential widespread conflict, which was realized in the Great War.
The underlying causes were exacerbated by treaties that compelled nations to support allies in conflicts, as seen in the Balkans leading to World War I. The Concert of Europe maintained peace for a period, but could not contain the growth of militarism, nationalism, and the rush to establish global empires. Lastly, the weakening of traditional powers like the Ottoman Empire in the face of rising nation-states in Europe contributed to the prevailing tensions that led to the Great War.