While Europe had been gradually getting rid of the complex of the trench warfare, what was manifested through return to the concepts of mobile operations of future war, the French military doctrine at the turn of 1920s and 1930s took a completely different perspective. It came from a number of social and political reasons, and resulted in reduction of conscription, gradual evacuation of the Ruhr Basin, construction of the Maginot Line, and gradual growth of the German military potential. France's military power weakened, and that conditioned the abandonment of the idea of an offensive on the first stage of a war, and return to the concepts of the position war. The main advocate of this concept was Marshal Philippe Pétain, and discussions over its issues lasted practically throughout the 1930s.
It was decided to organize the system of the national defence around the continuous line of fortifications along the eastern frontier, behind which the bulk of the armed forces had to wait for the enemy to bleed and allies to arrive. It was believed that a narrow front would be easily saturated with troops and equipment as it happened during the First World War. Such a situation would rule out any ability to manoeuvre, so the only efficient form of operations, apart from defence of course, could be only the operational break-through. In order to assure its success, advancing troops had to be saturated with appropriate quantities of artillery, infantry heavy weapons, and support tanks. However, such an operation would require a long period of build-up and unnecessary centralization of command. Contemporary French regulations attached a lot of attention to all the details, even the smallest ones, of the tactical command, and left no room for invention and initiative to the commanders on all the levels of the chain of command. It created the situation, in which the army, possessing a considerable potential to manoeuvre, was in fact immobile and incapable of efficient operating outside the scope of the mandatory schematics.
Of course, nobody expected that the erected system of fortifications would be impenetrable to the enemy forces. In such cases had to be engaged mobile reserves: motorized infantry and light mechanized divisions, whose designation was to plug breaches in the continuous front. Moreover, in case of violation of the neutrality of Switzerland and/or Belgium, there were planned mobile operations with rapid units, designated to defend the wings of the own strategic deployment. On the second stage of a war - after the enemy exhaustion - the French army had to switch to an offensive with the bulk of its forces, but an offensive conducted slowly, methodically, and meticulously preserving the continuous front.
Yet the most of attention was attached to the initial stage of a war. This problem was in details addressed by General Marie-Eugène Debeney. He postulated that behind the existing system of fortifications ought to be kept so-called army of coverage (armée de la couverture) with large peacetime establishments. Such an army, he argued, not only would be able to bring to a halt a surprise enemy attack, but also to undertake offensive operations already on the initial stage of the conflict. Under the coverage of its activities, the rest of the armed forces would have time to mobilize and concentrate for further operations. Also an officer of the General Staff, Colonel F. Culman, represented similar views, close to the official ones. Although they were correct in principle, the French army was not capable of quick response to initial challenge, due to its units' low peacetime establishments.
The system of fortifications, whose core element was the Maginot Line, and the military doctrine built around it, had brought the French military theory to an amazing passivity. At that time fortifications had been built all over the Europe; Germany had the Siegfried Line, Finland had the Mannerheim Line, Czechoslovakia had built a system of strong fortifications along the German border, but nowhere fortifications were regarded for a dogma, which dominated the whole military doctrine. In other countries they were just an element of a doctrine.