Which concept is associated with increased tensions and competition among European nations prior to WWI?

Militarism is the correct choice because it refers to the belief in building up strong armed forces to prepare for war. In the years leading up to World War I, many European nations engaged in an arms race, significantly expanding their military capabilities. This competition for military supremacy heightened tensions between countries, as nations sought to outdo one another in terms of weapons, soldiers, and naval power. The glorification of military strength contributed to a climate of fear and mistrust among the nations, fostering an environment that made conflict more likely.

The other concepts also relate to international relations but in different ways. Isolationism refers to a policy of remaining apart from the affairs or interests of other groups, particularly political affairs of other countries, which was not a primary characteristic of most European nations leading into WWI. Protectionism involves economic policies that protect domestic industries from foreign competition, which, while relevant to trade relationships, did not directly increase military tensions. Expansionism represents the policy of territorial or economic expansion but does not specifically address the arms buildup and military competition that characterized militarism in this pre-war period.