Final answer:
A key factor in the Allies' victory in the Battle of the Marne was their swift response to a German offensive, aided by the mobilization of reserves and the strategic use of taxi drivers to transport soldiers to the front lines.
Step-by-step explanation:
A key factor in the Allies' victory in the Battle of the Marne was their swift response to a German offensive. The German army had launched a major offensive to try to capture Paris, but the Allies were able to quickly mobilize reserves and reinforce their positions. In a remarkable display of logistics, the French government enlisted approximately 600 taxi drivers to transport soldiers from Paris to the front lines, helping to stop the German advance and eventually push them back.