Final answer:
The intense loyalty to a country that heightened tensions in Europe is termed nationalism, a sense of pride and superiority that sometimes escalated into rivalries and territorial conflicts, contributing to the buildup towards major conflicts like World War I.
Step-by-step explanation:
The intense loyalty to a country that caused much of the tension in Europe was called nationalism. Nationalism refers to the feeling of pride in and devotion to one's nation which sometimes resulted in a thirst for power and glory among European nations. Not only did it unify people, but it also spurred intense competition as countries sought to demonstrate their strengths and ethnic groups longed for autonomy. It also paved the way for the concept of self-determination as seen in the formation of nations like Belgium.
While patriotism may involve a love for one's country, nationalism often implies a belief in the superiority of one's nation over others. This belief led to a tension-filled environment in Europe where countries such as Germany, France, and powers within the Balkans held deep-seated rivalries. For multi-national empires like Austria-Hungary and the Ottoman Empire, nationalism posed a significant threat because it could lead to their disintegration.
The nineteenth century saw a change like nationalism as it was appropriated by conservative elites to maintain power. Moreover, it became associated with rivalry and resentment leading up to World War I. This situation was exacerbated by territorial conflicts, arms buildups, and the formation of military alliances such as those between France and its allies versus Germany and its allies.