At the time of the Revolution, France already had a population of 27 million. One hundred years later, its population had only increased to 38 million. Fix that, and 100 million is easy. For comparison, "Germany" around 1800 only had a population of 16 million, and unlike France, many millions of Germans emigrated to the New World in the 19th century. By the time of WWI, the German Empire had 66 mil. inhabitants, of which 57-59 million lived west of the Oder-Neisse line. At the eve of the Great War, France's population stood at 42 million.