France and Belgium had a defensive alliance after 1918. However, the construction of the Maginot Line in 1929-1932 and the total lack of a French response to the German remilitarization of the Rhineland in 1936 led the young king of Belgium (Leopold III) to cancel this alliance with France and declare Belgium a neutral country. Leopold III also invested in a new fortress at Eben Emael, to protect Belgian neutrality.
There is also a lot of wide spread misconceptions about the Maginot Line. Andre Maginot, was an interesting French politician. Born in 1877, he was already the under secretary of France's war department in 1914. He left this desk job and became a sergeant in the French Army. He was wounded at the battle of Verdun, in 1916. After the war, he was Minister of Pensions and did excellent work for the wounded French soldiers during the 1920s. He was also appointed the Minister of War on three separate occasions, in the rather chaotic Third French republic, during the 1920s.
Andre Maginot was born in Paris, but his family owned a farm near Revigay-sur-Ornain, in the Lorraine. This village was in the part of France that was not ceded to Germany after the Franco-Prussian war of 1870-1871, but Andre Maginot certainly heard about how the Germans burst through the Alsace- Lorraine during that war, before the French army was completely mobilized. This was not entirely true, but his father firmly believed it. Andre Maginot vowed never to let it happen again. The system of fortifications he ordered built in the Alsace Lorraine during his third term as Minister of War, were intended to shield those two provinces long enough for the French army to be mobilized. He said quite clearly, that it was not going to be the "Great Wall of France", but he died before it was even finished. Two major things happened after 1931. The French army came to believe it really was the Great Wall of France and most of the small eastern European Nations that had a series of military alliances with France : Romania, Czechoslovakia and Yugoslavia, plus Belgium, came to the conclusion that France would do nothing to save them, if Germany started another war. After the Munich agreement of 1938, they were correct in that assessment. Only Poland still trusted France would really fight, if another war with Germany broke out. The events between September 3rd 1939 and May 10th 1940 show that Poland was wrong.
Sources: "The Great Wall of France: The Triumph of the Maginot Line" by Vivian Rowe (1961)
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