The force that united people because they had similar languages, beliefs, and ideas and inspired them to fight outside invaders is **c) Nationalism**.
1. **Nationalism** is a sense of belonging and loyalty to a nation, often based on shared characteristics like language, culture, history, and values.
2. It can inspire people to come together, unite, and defend their nation against external threats or invaders.
3. Nationalism played a significant role in various historical events, such as the unification movements in Italy and Germany in the 19th century, where people rallied around the idea of a unified nation based on common traits to resist foreign domination.
4. Therefore, nationalism can be a powerful force that unites people under a common identity and motivates them to protect their shared beliefs and way of life.
