France's involvement in World War Two began in 1939 when, along with Great Britain, France declared war on Germany after the Nazi occupation of Poland. This marked the beginning of a war where the French military was largely ineffective in Europe. The results of which would see the Wehrmacht occupy Paris.
Before 1939 the French had pursued a policy of appeasement. This was a mistake while they had military superiority; however, towards the end of 1930s Germany's re-armament had gathered pace. By the late 1930s it seemed that the Reich's military had reached a degree of parity with the French, and France increasingly enhanced a series of fortifications on the German-Franco border, which was otherwise the Maginot Line.
At the 1938 Munich Conference French diplomats met with Britain and Germany to discuss Eastern Europe and Czechoslovakia. They hoped negotiation regarding Czechoslovakia could help avoid another potential war. An 'agreement' was reached pertaining to the Sudetenland. However, the Nazi occupation of the rest of Czechoslovakia violated the Munich Conference. Britain and France promised to defend Poland. As such, they declared war on the Reich in 1939 as German troops moved into Poland.
A period of relative military inactive followed. France continued to fortify the Maginot Line. It would not be until 1940 that France and Britain opened the Norwegian Campaign that aimed to cut Nazi oil supplies in Sweden. To prevent this, the Wehrmacht advanced into and occupied Norway. The French abandoned Norway, which became an occupied country.
Defeat here paved the way for the Battle of France that soon followed. The Wehrmacht bypassed the Maginot Line, and instead advanced through the Ardennes. The Germans exploited a weak point in the Allied line, and invaded France with heavy armory such as tanks and thousands of aircraft.
The Blitzkrieg was very effective, and the Wehrmacht moved towards and occupied Paris. This, combined with the occupation of Holland and Belgium, did not bode well for France's army that was increasingly encircled by the Germans. The French army became increasingly depleted, and with the BEF retreating towards Dunkirk the prospect of a counter-attack became more limited. At Dunkirk Britain evacuated most of the BEF, along with a few thousand French soldiers.
France was seemingly defeated. The Blitzkrieg had outmatched and outmaneuvered France's army. With the British conceding the battle was lost, the French established an armistice and Vichy France in the south.
However, De Gaulle did not recognize the armistice and organized the French Resistance in Britain. Thousands of Free French troops joined the British and provided extra military support for them in North Africa particularly during Operation Torch. Although France was seemingly defeated, De Gaulle felt otherwise; and as the war continued in the West another front in France reopened by 1944.
Allied victories in the East, North Africa and Italy paved the way for Anglo-American landings in Normandy. With the plans complete, Operation Overland began in 1944 as the Allies established a beach-head in Normandy. Free French troops joined the D-Day battle and provided some additional troops divisions for the Americans and British. By August 1944 the Allies had pushed towards Paris, and French troops combined with Americans against the remaining German soldiers as the Liberation of Paris began.
Here the Germans surrendered. Paris celebrated as the Allied armies passed through the streets in victory parades. Operation Overlord was now over, and a new French Republic emerged. Overall, the war in the West was seemingly won.
However, the Battle of the Bulge began in late 1944 around the Ardennes forest, as German reserves pushed the Allied armies back to Bastogne. Despite this, the Allies restored their lines and the troops moved further East out of France and into Germany. However, for the French Resistance the war was over.
France's involvement in World War Two largely ended in 1940. France's overall military contribution to defeating Germany had not been especially significant given the country's defeat in 1940. However, the French Resistance under De Gaulle had continued to provide military support to the Allied alliance beyond this, so in 1945 the Allies established a French occupation zone in Western Germany.