One example is the Austrian empire under Hapsburgs.
They had a huge empire before world war 1 all across Europe and managed to annex numerous states. Nationalism helped end it because the various ethnicities started rebelling against the empire and wanted to gain independence because the spirit of nationalism was flourishing at the time.
Another is the Ottoman Empire
They had a similar problem like the Austrians but at an even higher level because numerous parts of their lands were people who were not Muslims and who disliked them and liked their Christian tradition. This was seen for example in the Balkans where there were numerous insurgencies and independence wars spurned by nationalism.
Third can be the Russian empire under Romanovs.
The empire was huge and covered an enormous part of Europe and Asia. It included numerous countries with people of various backgrounds who wanted independence so they created many problems. As we know, the huge internal strife ended when the communists came and took the government from the royal family.
