Why Did France's Massive Maginot Line Fail in 1940?

The Maginot Line was an extensive series of fortifications built by France through the 1930s to protect its eastern borders from German attack. Stretching for over 200 miles (322 km), and including massive gun emplacements and extensive underground tunnels, the Maginot Line was rendered all but obsolete by the German attack through neutral Belgium and then north-eastern France in the opening stages of the Second World War(1939-45).