During the 1930s, the French had built the Maginot Line, fortifications along the border with Germany. The line was intended to deter a German invasion across the Franco-German border and funnel an attack into Belgium, which could then be met by the best divisions of the French Army. A war would take place outside of French territory avoiding a repeat of the First World War. The main section of the Maginot Line ran from the Swiss border and ended at Longwy. The area immediately to the north was covered by the heavily wooded Ardennes region. General Philippe Pétain declared the Ardennes to be "impenetrable" as long as "special provisions" were taken. If so, he believed that any enemy force emerging from the forest would be vulnerable to a pincer attack and destroyed. The French commander-in-chief, Maurice Gamelin also believed the area to be safe from attack, noting that it "never favoured large operations". French war games held in 1938, with the scenario of a German armoured attack through the Ardennes, left the military with the impression that the region was still largely impenetrable and that this, along with the obstacle of the Meuse River, would allow the French time to bring up troops into the area to counter an attack.
German invasion of Poland
In 1939, Britain and France offered military support to Poland in the likely case of a German invasion. In the dawn of 1 September 1939, the German Invasion of Poland began. France and the United Kingdom declared war on 3 September, after an ultimatum for German forces to immediately withdraw their forces from Poland was not answered. Following this, Australia (3 September), New Zealand (3 September), South Africa (6 September) and Canada (10 September) declared war on Germany. British and French commitments to Poland were met politically but they had adopted a long-war strategy and mobilised for defensive land operations against Germany, while a trade blockade was imposed and the pre-war re-armament was accelerated, ready for an eventual invasion of Germany.
French soldier in the German village of Lauterbach in Saarland
On 7 September, in accordance with their alliance with Poland, France began the Saar Offensive with an advance from the Maginot Line 5 km (3.1 mi) into the Saar. France had mobilised 98 divisions (all but 28 of them reserve or fortress formations) and 2,500 tanks against a German force consisting of 43 divisions (32 of them reserves) and no tanks. The French advanced until they met the then thin and undermanned Siegfried Line. On 17 September, the French supreme commander, Maurice Gamelin gave the order to withdraw French troops to their starting positions; the last of them left Germany on 17 October. Following the Saar Offensive, a period of inaction called the Phoney War (the French Drôle de guerre, joke war or the German Sitzkrieg, sitting war) set in between the belligerents. Adolf Hitler had hoped that France and Britain would acquiesce in the conquest of Poland and quickly make peace. On 6 October, he made a peace offer to both Western powers.