Napoleon brought so much hope. But he left. He came back, but then took so much more. When he departed a second time it was adieu, not au revoir. France was left disgraced.
However France wasn't only disgraced, it had a ticking time bomb, a stagnating population
Real Life Populations 1815:
France: 30m
England: 9m
Real Life Populations 1870:
France: 38m
England: 20m
Real Life Populations 1914:
France: 40m
England: 34m
France significantly hurt itself by having a stagnant population. The first serious results of this were shown in the Franco-Prussian War. However this requires a bit of an in-depth view to understand. In 1870 the population of Prussia and it's allies were relatively similar to France, around forty million. However Prussia and its allies had a VERY large relative youth population. This led to a massive economic edge. Prussia was able to beat France because of its massive industries and cutting edge weaponry.
But back to the alternate history. Let's say in 1815 or in the next few following years a policy was put into place to boost the population. Some may argue that this would actually be impossible. However the population density of France was VERY low (compared to many other European countries) in 1815, even though it had the highest population in Europe, sans Russia. Legislation that would encourage this would be tax breaks, assistance, and laws the would change the public attitude to having more children. Also the government could perhaps partially fund infrastructure to better cope with these new people. Now let's assume all of this policy more or less work, and assume the following would be the populations of France.
Alternate History Population of France 1870: 58 million people
Alternate History Population of France 1914: 79 million people
How would the time period that would be the Franco-Prussian war be different? How would the 1900's be different for France?