Why did nationalism increase when napoleon conquered?

They didn't. The Peace of Westphalia in 1648 did, strictly speaking.

Well nationalism has it roots in French Revolution, at late XVII and at begining of XIX century some nations began to feel it national pride, before that countries just were loyal to king, there was beleaf that kings power was given by God, that was apsolutistic monarchy...When French revolution ocured, people was angry and miserable for bad life, while aristocracy lived good, so as the church. French revolution bolished king, and putted people as prime, that is diference between monarchy and republic, republic belogns to people while monarch at least in those days were property of king and aristocracy not people...So when Napoleon came to power, people were thinking he is the descendence of French revolution...Ofcoures Napoleon disminished the Inquisition that was one of mechanism of repression and terror...When Napoleon wars happened, some of major empires that had kept other nation in bondage for many years were busy fighting Napoleon...That gave opening to some nations to form national identity, and to fight their captors....So end of XVIII and begining and middle of XIX was time of revolution and nationalism...So during 1804 to 1813 we have Serbian revolution that fights Turkish Otoman empire that lead Greece to fight also Turks and some of Balkan nations, than middle of XIX century Oto von Bismark unified Germany, than Garibald united Italy...Anyway nationalism was creation of national fealing trow Europe, thanks to Napoleon wars...