France "entered" WWII because France and Britain had an alliance with Poland that said if Poland should be attacked then both Britain and France would declare war on the aggressor, which just happened to be Germany.
Why France actually bothered declaring war is an interesting question because the German army swept through to Paris in about 40 minutes, and once they were there told the French either to surrender or their beautiful Paris would be reduced to a crater. So they surrendered immediately, and installed a puppet government known as Vichy under Marshall Petain that did what the Germans told it to do, which included rounding up French Jews for deportation to the death camps. Petain was at one time sentenced to death for treason, but his death sentence was commuted by de Gaulle after the war.
Many patriotic Frenchmen (and an enormous number of women) ran an efficient underground movement returning downed allied pilots back to England, and running sabotage cells against German installations. Many of them were subjected to months of the most hideous of Gestapo tortures, and many of them to death, without revealing crucial information. We owe them a great debt of gratitude for their bravery. If we were to ever find out their names, the French book of war heroes would undoubtedly be thicker than it is.
There is more about Vichy here: http://en.wikipedia.org/wiki/Vichy_France Phil
Poland
The United States entered the war in April 1917 on the side of France, Great Britain, & Italy to defeat Germany in November 1918.
try this website http://www.conservapedia.com/Debate:Should_the_United_States_have_entered_World_War_II%3F
France entered the war with hopes of achieving a lasting victory against their major colonial rival Britain.
France
they started it
The US entered the war for a variety of reasons
They didn't? You're thinking of World War II.
France
Poland
The United States entered the war in April 1917 on the side of France, Great Britain, & Italy to defeat Germany in November 1918.
France was about to be overrun by Germany. A good reason to go to war ??
The Jet engine entered service around 1944 towards the end of World War 2 Concord entered service in 1976 with British airways and Air France World War 1 ended in 1918, So no.
Italy and France
The British turned their attention to the Southern colonies when France entered the war in 1778
Britain eentered a treaty with France and the Russian Empire; when they were entered into the war, Britain had (and wanted) to follow.
When Germany invaded Poland in 1939, France and Britain, who had promised aid to Poland if Germany invaded, entered the war on the Allied side, thus starting the Second World War.