Nationalism united people into nation- states, toppled empires composed of many ethnic minorities, and contributed to the outbreak of wars in the nineteenth century. how would you evaluate this statement?

This statement would be more or less correct I would say. 

Nationalism inded did develop strongly in the 19th century, and also in a lot of cases led into the development of nation states. At the same time, powerful empires that existed in those times had often many different ethnic and political groups in their borders. All of these factors often led to different wars that were quite horrible.