After the quick collapse of the French military, Britain itself was under a threat of a German amphibious invasion, and was attacked by the full force of the German Luftwaffe.
The pre-war pacifist strategy, military weakness, and anti-Communism of Britain and France led Stalin in August 1939 to decide that making a deal with Hitler is a better way to protect Russia from Hitler than making an alliance with Britain and France against him.
When the small Norwegian military, and British forces which landed in northern Norway to help them, failed to stop the Germans, the king and government were evacuated to Britain, and Norway remained under German military occupation until the end of World War 2.
The result was that the British Air Force could then recover, keep fighting effectively, and win the battle, keeping Britain from invasion, and denying Hitler victory in the West.
Three months later, in the peak of the Battle of Britain, when the German Air Force was getting close to breaking the smaller British Air Force, Hitler changed the objective of the German Air Force from defeating the British Air Force to killing the people of London in an air bombardment campaign.
So the most powerful units of the German army had to idly watch from short distance as the core of the British army was allowed to escape from a hopeless situation.
In June, when allied defences in France and Belgium collapsed, he ordered his tanks not to attack the British force of 338,000 soldiers besieged on the beach at Dunkirk.
King George II of the politically unstable Greece and his dictatorial prime minister Ioannis Metaxas insisted to remain neutral in World War 2, and repelled an Italian invasion which followed, but in 1941, shortly after Metaxas' death, the mighty Germany military came to help the weak Italian invaders and, despite support by a British military force, Greece was occupied by the Germans until it was liberated by the British in 1944.
De Gaulle's appointment was much too late to save France, and when France surrendered, De Gaulle fled to Britain and led the "free French" forces until the end of the war and later became post-war president of France.
Persistent Norwegian resistance, and Hitler's worry of a second British landing, made him keep a huge garrison of 300,000 German troops in Norway until the end of the war, practically reducing this massive force from the German army's order of battle.
The mighty American industry went into full war production effort which dwarfed those of both allies and enemies, allowing the relatively small US military forces to rapidly grow to a mighty force, and defeat Japan and help Britain and Russia defeat Germany and Italy.
Edvard Benes was the elected president of Czechoslovakia between 1935 and October 1938 when he resigned when the appeasement policy of his French and British allies led them to support Hitler's demand to annex parts of Czechoslovakia.
The destructive surprise attack ended American isolationism and the US joined the war and allied with Britain and Russia to defeat the aggressors Axis of Nazi Germany, militarist Japan, and Fascist Italy.
Despite the strong sympathy of the American public in support of Britain and against Nazism, only an attack on the US could persuade the American public to go to war.
Aware of this vulnerability, the Germans developed and used an expensive industrial process to produce alternative fuel from coal and other materials, but even so, the German military, especially the Air Force, was always critically dependent on Ploesti's oil, and British and Russian military planners knew it.