The Fall of France by Julian Jackson thoroughly examines a pivotal moment—or, more accurately, a series of important events—during World War II. The book's thesis argues the importance of France as an Ally stronghold, and Jackson opines that its loss and eventual occupation by German forces prolonged the war. France was a vital territory for the Allies due to its central location, wealth, and population.

Logistically, France created a buffer between the United Kingdom, the other important stronghold of the Allied Powers, and the rest of continental Europe. The book goes into great detail examining the series of events that occurred prior to France's defeat by the German military. For instance, political infighting weakened the government of France and allowed the Nazis to manipulate certain French politicians.

Jackson cites various errors made by French military officials—despite the fact that the French military had, at that point, more experience in warfare than the Germans. Jackson also discusses social factors that led to the weakening of the French political structure and resistance capabilities in general, such as the low morale of both the general populace and the French troops.

Another possible reason Jackson gives for the French defeat is the decadent lifestyle in France between World War I and World War II. Like the United States and Britain between the two world wars, France experienced a transition towards a materialist society where wealth and luxury were emphasized. On the other hand, the German people suffered tremendous economic woes during the interwar years.

After an embarrassing defeat in World War I, German citizens—among them Adolf Hitler—felt a collective chip on their shoulders. They not only felt ashamed and resentful as a nation but also endured poverty and joblessness, which was in contrast to France's decadence and apathy. Essentially, the loser of the previous war developed a Spartan mentality, whereas the victors became complacent and comfortable in their positions of global power.