The film “Darkest Hour” shows us how Winston Churchill became Prime-Minister and how he faced his first dilemma as such: to start peace negotiations with Germany or fight it until the Victory was reached (or die trying). The situation was far from easy. British army was on the verge of total annihilation and, at the time, the German army was apparently unbeatable. All seemed lost and hopeless. Except that Churchill was a great wordsmith. It was the power of his words that galvanized a whole nation (a frighten nation) and led them to resist and then fight the mighty German army.
We can see this film as a complement of other films about World War II. The directors didn’t intended to do so, but if you watch enough films on this topic you start to have a very good idea about what really happened. Here are some examples, related with references in “Darkest Hour”:
The “Dynamo Operation” is portrayed in the film “Dunkirk”.
The King we see talking with Churchill is King George VI, father of Queen Elizabeth II – he’s portrayed in the film “The King’s Speech” [by watching it you can understand the issue of Wallis Simpson and the slight stutter of the King].
“Suite Française” is a film that portrays the flight of people from Paris upon the invasion of the German army [it’s based on a book written almost in real time by a well-known Jewish writer, Irène Némirovsky, who died in a concentration camp and couldn’t finished it].
Other films on this topic that may interest you:
“Saving Private Ryan”: shows a little of what the Normadie Landings were like, the turning point of the war and the beginning of the end for the German army.