Second World War 1939-45

Germany invaded France in 1940, overwhelming French defences in the "Maginot line". The defeated Br and Fr armies troops retreated across the Channel in the Dunkirk Evacuation, while the Fr government surrendered. The Germans used Nord-PasdeCalais as a base for continuing the attack on Britain: by air in the Battle of Britain and then by heavy bombing raids on cities.
USA joined the war in 1941. Germany built almost impregnable defences along the Channel coast - the Atlantic Wall. In 1943-4 Germany built bases in N.France to launch V1 and V2 rockets in an attempt to save the war.
Nord-PasdeCalais was liberated in 1944 after the Normandy Landings. Meanwhile they endured 4 years of occupation - the Resistance was particularly active in the north - the birthplace of Free French leader-in-exile, Gen.de Gaulle.

More information:
Second World War in more detail
Dunkerque
Atlantic Wall
Blockhaus rocket base
La Coupole rocket base
Gen.de Gaulle museum