How did nationalism motivate the french against the germans

When the leaders of European New Right parties met on January 21st 2017 in the German city of Koblenz, many were surprised that nationalist politicians could attempt to work together and actually talk about international cooperation. An international nationalist meeting? To many, it at first sounded more like an anachronistic oxymoron than an actual political event taking place in the 21st century. However, when one looks back in time, the histories of European nationalist movements in general, and French and German nationalism in particular, are intertwined. So much so that one could even speak of a common history.