When the German Operation Marne-Rheims ended in July, the Allied supreme commander, Ferdinand Foch, ordered a counter-offensive, which became known as the Second Battle of the Marne.

After the Germans had lost their forward momentum, Foch considered the time had arrived for the Allies to return to the offensive.

The British Expeditionary Force (BEF) had been reinforced by large numbers of troops returned from the Sinai and Palestine campaign and from the Italian front, and by replacements previously held back in Britain by Prime Minister David Lloyd George.

The Picardy terrain provided a good surface for tanks, unlike in Flanders, and the defences of the German 2nd Army under General Georg von der Marwitz were relatively weak, having been subjected to continual raiding by the Australians in a process termed peaceful penetration.

[15] On 10 August, the Germans began to pull out of the salient that they had managed to occupy during Operation Michael in March, back towards the Hindenburg Line.

[20]: 125  The British Fourth Army approached the Hindenburg Line along the St Quentin Canal, during the Battle of Épehy (18 September).

Foch planned a series of concentric attacks on the German lines in France (sometimes referred to as the Grand Offensive), with the various axes of advance designed to cut German lateral communications, intending that the success of an attack would enable the entire front line to be advanced.

[11]: 205–6  The main German defences were anchored on the Hindenburg Line, a series of defensive fortifications stretching from Cerny on the Aisne river to Arras.

[20]: 123  General Rawlinson wrote, "Had the Boche [Germans] not shown marked signs of deterioration during the past month, I should never have contemplated attacking the Hindenburg line.

The evidence of failing German morale also convinced many Allied commanders and political leaders that the war could be ended in 1918; previously, all efforts had been concentrated on building up forces to mount a decisive attack in 1919.

The Allies pressed the Germans back toward the lateral railway line from Metz to Bruges, which had supplied the front in northern France and Belgium for much of the war.

As the Allied armies reached this line, the Germans were forced to abandon increasingly large amounts of heavy equipment and supplies, further reducing their morale and capacity to resist.