The correct answer is B) revolutions and nationalism.
Political boundaries of the 19th-century Europe countries frequently changed due to revolutions and nationalism.
Small countries came and went from one territory to another due to revolutions, as it happened with Prussia and Italy. Nationalism played a key role in forming nations in that similarities in identity and race allow the formation of other countries. The French Revolution influenced many ideas that were followed by other nations. Many countries confronted the authority of the monarchy and demanded changes in politics and the economy under strong nationalist ideals. Countries formed after independence movements such as the case of Poland, Romania, and Bulgaria.
