Only at the very end of the Napoleonic Wars did the fortified frontier of Vauban begin to exert a strong strategic influence; most of Napoleon's campaigns took place beyond French borders. However, after the Grande Armee disintegrated in Russia and was driven out of Germany, Napoleon finally had to fight on his home turf.

The many fortresses (103, from Dunkirk by the sea to Huningue against the Swiss border, in three rows) guarding France presented Napoleon with a major dilemma. On the one hand, garrisoning them would be a massive drain on manpower, and would not leave him much left over to form an active field army. On the other hand, if the field army was prioritized, many of these fortresses would fall into enemy hands without much resistance. Napoleon only had about 60-70,000 men for the defense of France, whereas the Coalition had something closer to 300,000.

Indeed, Blucher's chief of staff, Gneisenau, noted that French fortresses were altogether lacking in everything needed for a successful defense, and based his plan for an invasion of France over the Lower Rhine on this inadequacy. Essentially, he planned to take Blucher's army to Maastricht, where he believed it could threaten many French fortresses simultaneously, and force Napoleon to fritter away precious manpower manning them. This would allow the rest of the Coalition forces to decisively overpower Napoleon's field army and strike at the heart of France.

The invasion of France promised to be the decisive campaign of the war, so numerous generals and staff officers submitted their proposals. Most of them had to make allowances for the French fortifications along the frontiers. For example, the Bavarian Wrede wanted to make immediate surprise attacks on the poorly manned fortresses, in opposition to the King of Prussia's adviser, Duka, who wanted to go into winter quarters and undertake a campaign of methodical sieges against the frontier fortresses in spring. Radetzky, the Austrian chief of staff wanted to circumvent the French fortress line in the east as much as possible and invade over the upper Rhine, near Switzerland.

In fact, the French fortresses probably did more service as a subject for debate in Allied headquarters than they did as military obstacles. The Allies spent so long debating, and later moving armies into position to circumvent, dealing with the fortresses that Napoleon was able to regroup his disintegrating army behind the frontiers. When the allies finally did cross the Rhine, Napoleon was able to defeat them in several battles, despite longer numerical odds than ever before in his career, though in the end he was still forced into exile.