Why did nationalism backfire for Bismarck

United Germany under Prussian rule by means of "blood and iron", came from Prussia's junker class (nobles) was prime minister for King William I but then became chancellor, master of realpolitik, NOT a German nationalist, rather his loyalty was to Hohenzollerns (ruling dynasty of Prussia) main goal was to bring more power to the hohenzollerns, strengthened army and led Prussia into 3 wars which increased Prussia's prestige and paved the way for German unity