The Ligne Maginot (Maginot Line) was named after the French Minister of War André Maginot who planned the fortification. Built was actually only the part along the borders to Germany and Italy, the rest was skipped, and as a result it was a complete fail. In 1940 the German army occupied France in a few days by travelling through occupied Belgium and the Netherlands. The line became a metaphor for expensive efforts for a false sense of security. Merriam Webster defines the term Maginot Line as: "2: a defensive barrier or strategy that inspires a false sense of security".
The problem with border fortification is always the same, this applied for the Chinese Wall, the Roman Limes, and any later fortification. It is always only as strong as its weakest part. Once it is broken at one point, the enemy will attack from behind, or simply ignore the fortification while conquering the country behind. And if the defender is forced to move his troops from the defensive line, it is far easier to destroy. The French Maginot Line was
The Maginot line was built between 1929 and 1938. Most forts were completed many years before the war, and they were not staffed or only with maintenance staff. But when World War II started officially in 1939, the whole fortification was staffed with regular soldiers and reservists. The Maginot Line was invulnerable to aerial bombings and tank fire, had underground railways as a way to move men and material. It also had state-of-the-art living conditions for garrisoned troops, supplying central heating and eating areas for their comfort. It also was electrified. The generators were needed for many purposes, including telefone, water pumps and air filters.
The time between the beginning of the War in 1939 and the actual invasion is called Phoney War, in French Drôle de guerre. The actual invasion in June 1940 is today called Battle of France, also known as the Western Campaign, the German term was Frankreichfeldzug (Campaign against France). The Maginot Line was impervious to most forms of attack, and consequently the Germans invaded through the Netherlands. What followed were minor quarrels between German soldiers and the forts of the Maginot Line. But actually the Germans were already in the hinterland and troops and material were taken from the forts for the actual battle. Finally, an armistice was signed on 22-JUN-1940 in Compiègne and went into effect two days and six hours later, at 00:35 on 25-JUN-1940. Most fortifications surrendered in the next three days, the Maginot line collapsed and was taken over by the Germans. The Battle of France had taken only six weeks, despite the Billions invested into the Maginot Line. It was the foundation of the German invincibility.
Most fortifications had their first military action in 1944, when the Allied forces invaded. Again most of the line was bypassed, but there were some heavy retreat battles near Metz and in northern Alsace. The forts were less effective, because they were built against the enemy in the east, the western side was their back.
Then the Germans tried to regain some ground and started Operation Nordwind in January 1945. At this time, the Maginot Line casemates and fortifications were utilized by Allied forces. And so a part of the line was actually used for the purpose it had been designed for and showed what a well-designed fortification it was. On the other hand, by this time the German army was almost defeated, and this last attack was carried out by the Volkssturm. This was a ramshackle army of children and old men who had been forced into military service and had no appropriate equipment.