After the Battle of the Frontiers, the right and center wings of the German army sweep into France. The French retreat in a rearguard action, trying their best to slow the German advance so the French can regroup. Meanwhile, the defenses of Paris have not been completed, and Joffre orders two defensive divisions to reinforce the front. The French government, like the army, is in shambles, replacing ministers and commanders every few days. While the French fall back, the civilian government attempts to protect Paris. The Germans follow the French retreat too quickly. The British army is fighting a rearguard action as well, gaining time for the general retreat, though British leaders are also considering how to save their armies. In a battle near the French town of Le Cateau, the British, fighting against superior German numbers and supported on their right flank by the French, are able to gain that time, though the British losses reinforce the thought that their armies should be taken home.

As the French attempt to regroup, German forces continue to move forward lest they let the French form a new battle line. However, German forces have been thinned out—some have been left behind to hold conquered territory, some have been sent to the Eastern Front and Tannenberg, and many have died—so there are gaps in their lines as they move forward, hoping to reach Paris and end the war.