Nationalism is a political ideology that emphasizes the importance of a shared national identity, culture, and history. It aims to promote national consciousness, which means the feeling of belonging and loyalty to one's own nation.
Nationalism can help promote national integration and unity within a country, as it encourages people to come together and work towards a common goal. However, it does not necessarily promote secession or splitting up a country into smaller parts. In fact, nationalism often emphasizes the importance of preserving the territorial integrity of a nation-state.
Therefore, the option that nationalism does not ensure is secession in a country. While nationalism can promote the idea of self-determination and independence, it generally does not support the breakup of a country.