Why did the Napoleonic Wars represent a watershed in the history of warfare?
1 Answer
Because in those wars the keystone of the French Army was a meritocratic infantry of citizens, reminding that of Republican Rome. And because a division could act autonomously.
Explanation:
For a more extensive discussion of the subject, you may read at this source
Napoleon and Military Innovations
In fact before Napoleon, all the armies were led by officers from the nobility without test of abilities and the subaltern ranks were filled by some kind of impressment. The higher ranks were not open to the plebs. Alternatively there were mercenary troops with no allegiance to the country they fought for.
The division's autonomy meant that wise junior officers or non-commissioned officers could grab opportunities or quickly adapt to the local conditions and demands.