The growth of Prussia in the 19th century and after 1871 into early 20th century led to contention between Germany and France. The German Empire altered the balance of power in between France and Germany which became main reason of conflict between them.
Explanation:
Germany, excluding Austria, was united after French defeat by Prussian in 1870. The forces of Prussia and Germany united and fought several battles with French army. But French side lost these battles. All these led to disputes between France and Germany writers, historians and politicians.
In times before French Revolution, French and Prussian had respect for each other even though they were fighting each other as at that time conflict was between authorities and not between people.
But at the time of French Revolution, there was a beginning of nation formation in Europe. This let to conflict between people of nations also rather than keeping it limited to authorities only.
This started conflict between France and Germany.