Final answer:
Nationalism is the political movement focused on the self-determination and autonomy of a nation, characterized by a shared identity based on culture, history, and territory.
Step-by-step explanation:
The political cause along ethnocultural lines seeking to control their own affairs is best defined as nationalism. Nationalism is a political ideology that emphasizes the unity and interests of a nation, often advocating for the right to self-determination and political autonomy. This sense of pride in and celebration of a national identity is usually based on shared attributes such as culture, history, and territory and can be a powerful force in shaping a nation's policy and identity. During the 19th century, nationalism became a significant movement as various ethnic groups desired autonomy and the formation of nation-states based on common characteristics like language, ethnicity, and religion, with the ultimate goal of self-governance.