I didn't know that. Was this made possible by a societal change?
No, it wasn't.
Well, you asked for it.
All of the sources of the French overhaul of their military systems and doctrines were the product of their experiences in the War of the Austrian Succession (and to a much lesser extent, the American Revolution) and an uncommon recognition of the genius of serving officers in a period of roughly 1730 to 1780. One of the most colorful figures of the late 17th and early 18th centuries in Europe was Augustus the Strong, hereditary and Electoral Duke of Saxony and elected King of Poland. His oldest (bastard) sone was Moritz, known as Moritze von Sachsen, or, to the French, Maurice de Saxe. He first marched off to war at 12 in the War of the Spanish Succession (1700-1713). By the time of the War of the Austrian Succession (1740-1748), he was a gouty old man who could no longer sit a horse, and tore around the battlefield in a little buggy. He was a genius. He fought two great, bloody battles against the Army of the Pragmatic Sanction, nominally lead by King George II of England, and until Maurice beat 'em up, the most successful army to that time in the war. At Fontenoy, he tore back and forth between his commanders, and sent his regiments out on individual axes or operation as the situation demanded. He had already written Mes Rêveries
, but it was not published until after his death. It is, arguably, the most influential book on warfare ever written (up yours, Tsun Szu).
During that war, the French invaded the Kingdom of Sardinia, which was the island of Sardinia and the northeastern portion of Italy. That northeastern portion of Italy was known as Piedmont, and the French wanted to knock them out of the war. General Bourcet planned the invasion, and his plan was another brilliant use of separate operational axes. Invading Italy from France was difficult because a small number of defenders could hold up the attackers in the mountain passes of the Maratime Alps. Bourcet solved this problem by sending the army in in nine columns, any one of which outnumbered the defenders. Each column commander was instructed to put pressure on the defenders, but if informed that any column to his right or left had successfully infiltrated the passes to his right or left, he was to leave a screen and move by his right or left, as the situation dictated. The Franco-Spanish army arrived on the plains in the heart of Piedmont in two weeks, with minimal casualties as the defenders retreated in disorder, unable to deal with what was to them a bewildering and incomprehsible operation. The French and Spanish managed to lose all the value of the campaign by bickering, but that did not lessen the value of the lessons learned.
The principle lessons they learned from the American Revolution were in the use of light infanty and skirmishers. All of lesson were taken to heart by Frech military men, and Saint Germain who was Louis XVI's war minister in 1775 began the process of the review of French militay doctrine. He died in 1778, and was generally hated by an aristocratic officer corps, because he wanted to reduce the numbers of officers and rationanlize the organizational structure. Nevertheless, the reforms he started were carried forward by de Broglie, and when Napoleon was a snot-nosed child at Brienne, and then a student at the Ecole militaire in Paris, the new doctrines were being refined and taught.
New drill was introduced, and the soldiers were taught to march in three kinds of columns--march columns, "waiting" columns and columns of attack--from which they could deploy into line as necessary. The units were organized in the tripod system (used by the U.S. Army in the Second World War), with three "divisions" (what we would call companies) forming a battalion, three battalions forming a regiment and usually (but not invariably) three regiments forming a division (as we understand the concept of an army division). The battalion was the basic unit. It would deploy with a company to right and left, and a company in reserve. The reserve company would send half its number out in front of the line as skirmishers. If the enemy approached close enough to threaten the skirmishers, the remainder of that company would advance through the interval (a gap left between the left and right companies) to form a line on which the skirmishers could fall back. The reserve company could then fall back to its reserve position, or form to the right or the left, or form in the interval to produce a line from all three companies. The battalions of a regiment could operate in the same way, and the regiments in a division could perform in the same manner. It gave the army marvelous flexibility, and it was used to great effect against the Austrians, Prussians and Brunswickers in the Wars of the French Revolutioon before Napoleon came to power. Them boys just didn't understand what was happening, and what the French were doing just look like confusion to them, but they were still getting their asses kicked.
Teaching the officers to operate on an axis dictated by local conditions meant that a battalion or regiment could move to face an attack or to lauch one without reference to the behavior of the battalions or regiments on their flanks--it was the responsibility of higher command to assure that their flanks were not left "in the air." A march column could be moved to the side of the road and doubled up (made twice as wide) to become a waiting column until the unit were needed, or lauched as an attack column using the weight of the mass of men to break the enemy line, which was especially effective if they could be launched at the enemy flank.
The higher order organizational changes meant that each regiment had a staff with an intelligence officer, a commisary officer, a quartermaster, an ordnance officer, etc., etc.--all the offices of a modern army as we now know them. All of these regimental officers were responsible to the officer of the division with the same responsibilities, who was in turn responsible to the officer of the corps with those responsibilities, who was in his turn responsible to army intelligence, commisary, quartermaster, ordnance, etc. This was the part which Napoleon exploited so brilliantly, because he was an organizational genius. That was how he was able to launch his grand armies of hundreds of thousands of men, on foot, across hundreds of miles of any type of landscape Europe could offer, and arrive before the enemy barely knew he was moving.
The Wagram campaignn was the most brilliant expression of this ability, and also the best example of Napoleon's total lack of tactical command skills. Having rolled the Austrian army down the Danube, reeling from the speed of the French advace, he halted, waiting weeks, and then attacked them head-on. He won the battle of Wagram, but at the cost of his best veteran officers, non-coms and private soldiers. Commanding directly on the battlefield, Napoleon was hopeless.
The Prussians completely revised thei military doctrine in 1813, and the document they produced showed that they learned absolutely nothing from the wars with Napoleon--they just didn't get it. The English, of course, just decided that nobody had anything to teach them, and didn't ever seem to have learned anything from the experience. The Americans enthusiastically embraced the new doctrines, and even though the Europeans sneered, the armies which fought our civil war were as modern and well-organized as any on earth. Despite continuing worship of the Prussians by historians, the United States Army in 1865 was superior any on earth, the Prussians and the French included.
Today, military organizations take for granted the innovations the French credated in the late 18th century. Before de Broglie, modern staff systems simply didn't exist. These days, people take them for granted, and hardly know what i'm talking about when i try to explain it to them.