The Phoney War was an eight-month period at the start of World War II during which there was only one limited military land operation on the Western Front, when French troops invaded Germany's Saar district. Nazi Germany carried out the invasion of Poland on 1 September 1939, and the Phoney period began two days later with the declaration of war by the United Kingdom and France against Germany, after which little actual warfare occurred, and ended with the German invasion of France and the Low Countries on 10 May 1940. Although there was no large-scale military action by Britain and France, they did begin some economic warfare, especially with the naval blockade and shut down German surface raiders. They created elaborate plans for numerous large-scale operations designed to cripple the German war effort. These included opening an Anglo-French front in the Balkans, invading Norway to seize control of Germany's main source of iron ore, and an embargo against the Soviet Union, which supplied Germany's main source of oil. By April 1940, the lone execution of the Norway plan was considered inadequate to stop the German offensive.

The Saar Offensive was the French invasion of Saarland, Germany, in the first stages of World War II, from September 7 to October 16, 1939, in response to the German invasion of Poland on 1 September 1939. The original plans called for 40 divisions, and one armored division, three mechanised divisions, 78 artillery regiments and 40 tank battalions to assist Poland, which was then under invasion, by attacking Germany's neglected western front. Despite 30 divisions advancing to the border, the attack did not have the expected result. When the swift victory in Poland allowed Germany to reinforce its lines with homecoming troops, the offensive was halted. French forces then withdrew amid a German counter-offensive on 17 October.