Final answer:
Economic competition was a source of tension between European powers before World War 1, as nations vied for colonial expansion, industrial dominance, and military superiority, which were exacerbated by nationalist movements and the decline of multi-ethnic empires.
Step-by-step explanation:
The source of tensions between European powers before World War 1 that fits best from the options provided is B. Economic competition. This tension arose due to the rivalry between Europe’s great powers who were vying for economic dominance, industrial growth, and global empires. A significant factor contributing to this was the desire for colonial expansion, where Germany’s aspirations, particularly for more colonies and a larger navy, brought it into direct competition with the established British Empire. The industrial and military advancements of the era meant that these rivalries grew into an arms race, further increasing suspicions and tensions.
The collapse of the Ottoman Empire and the drive for nationalism were also sources of tension. As multi-national empires like the Ottoman Empire and Austria-Hungary began to disintegrate, the desire of different nationalities to create their own nations added to the political instability.
All these factors, combined with intricate alliances and treaties, created a powder keg scenario where a single incident, such as the assassination of Archduke Franz Ferdinand, could and did lead to a full-scale war.