After the Americans entered WWII they had to decide where to fight first in Europe. North Africa was split into three parts. Egypt was held by the Allies, the section from Tunisia to Libya was held by the Germans and the western part was held by Vichy France which was neutral. The Americans with the aid of the British invaded the NEUTRAL Vichy held western part of North Africa. The Allies did encounter some resistance but were able to prevail with relative ease. They were actually hoping for no resistance since Vichy France was friendly with the the United States. In retaliation the Germans occupied what was left of unoccupied France in Europe. This was the end of Vichy France and French politicians were forced to choose sides. The Allies used this position in North Africa to attack the Axis in North Africa from the west. This was also just after the time when the British scored their first big victory in  El Alamein and they proceeded to attack the Germans in North Africa from the east.

(Book – The Second World War Volume 4 – Winston S. Churchill)