A War of Weeks

The point of divergence lies in the late 1930s. Alarmed by German rearmament, France reorganized its army around armoured divisions, equipped its tanks and command posts with radio, modernized its air force and adopted a doctrine of rapid offensive action. When Germany invaded Poland on 1 September 1939, France and Britain declared war on 3 September, and this time Paris honoured its promise to Warsaw to attack quickly and in strength. Germany entered the war expecting the western powers to remain passive. Nearly all of its panzer and motorized divisions and most of its air force are committed in Poland. The western frontier is held by roughly thirty-odd divisions, many of them reservists and second-line formations, behind a Westwall that is incomplete in several sectors. Civilians have been evacuated from a red zone along the Rhine and the Saar. Ammunition, fuel and raw-material stocks were sized for a short campaign, and the British naval blockade has already cut most overseas imports. Romanian oil and Soviet deliveries promised under the new German–Soviet trade arrangements are Germany's main outside sources. Within the officer corps, men who plotted against Hitler during the Munich crisis of 1938 still hold senior commands. Poland has been fighting alone for a week. Its armies are retreating toward the Vistula, the Narew and the San, the government is evacuating eastward, and the commander-in-chief has moved to Brest, with communications between headquarters and armies breaking down. Polish planners hope to hold a redoubt in the southeast next to allied Romania while France and Britain relieve the pressure in the west. On 23 August Germany and the Soviet Union signed a non-aggression pact whose secret protocol divides eastern Europe into spheres of influence, with a line through Poland along the Narew, the Vistula and the San, and with the Baltic states and Bessarabia also concerned. The Red Army has begun a partial mobilization in its western military districts. Britain is at war but has almost no ground forces on the continent. Its Expeditionary Force is preparing to cross the Channel, its advanced bomber squadrons are already in Champagne, and the Royal Navy dominates the North Sea. Italy has declared non-belligerence despite its alliance with Germany. Slovakia has joined the attack on Poland. Hungary, Romania and Yugoslavia want to stay out of the war while guarding their own territorial claims. Belgium, the Netherlands, Luxembourg and Switzerland have mobilized to defend strict neutrality, and Belgium refuses to let French troops cross its territory. In the United States, the Neutrality Act still bans arms sales to the belligerents, and President Roosevelt is seeking its revision.

At dawn on 7 September 1939, a French army rebuilt during the late 1930s, with armoured divisions, radio-equipped tanks, a modern air force and an offensive doctrine, crosses into the Saar and the Palatinate at full strength. Germany is one week into its invasion of Poland: Kraków and Katowice have fallen and the Polish Corridor is cut, but Polish armies still hold Warsaw, Łódź, the Narew line and the coast at Gdynia and Hel. The Westwall is manned largely by reserve divisions, the Wehrmacht's strongest formations are in the east, and Germany faces the two-front war it gambled on avoiding. Moscow, Rome and the neutral capitals watch to see which way the balance tips.