Germany had already used Belgium as an invasion route in 1914. Belgian troops had fought hard, but they were eventually overwhelmed, so French planning could not safely assume Belgium would absorb another German attack. A strong fortified border would offer a more reliable delay. Hardwired telephones could keep the defenders connected, while radio-equipped mobile units moved to reinforce them. The passage links fortification design to communications and confidence in army command.
Notable Point · 1:46-3:24
Belgium and the need for a hard border
Germany's 1914 route through Belgium shows why plans had to account for known enemy behavior instead of relying on hope.