Why did the concept of nationalism threaten the large European empires?

The concept of nationalism threatened large European empires because it emphasized the idea of self-determination and ethnic identity, leading various national groups within these empires to seek independence or greater autonomy. This challenge undermined the political cohesion of multi-ethnic empires, such as Austria-Hungary and the Ottoman Empire, as diverse groups began to assert their distinct cultural identities and aspirations. Additionally, nationalism fostered competition among nations, which heightened tensions and contributed to conflicts, ultimately destabilizing the existing imperial structures.