On the outbreak of WWII the British prime minister Chamberlain is replaced by Winston Churchill, without much enthusiasm of his own party. Especially when Churchill’s rhetoric is about fighting rather than trying to make peace, ways to get rid off him are soon thought of.
Starting optimistically it soon becomes clear that Churchill has to admit that he cannot overpower Germany and when 300.000 of his troops get trapped at the French border, an unpopular way of evacuating them is started (this evacuation is what the film Dunkirk is about).
Some of his ministers want to make peace with (meaning: surrender to) the Germans, but as the people seem to prefer fighting over flying, Churchill pushes his old tactics again.
The film makes a nice history lesson showing a hard politician who was also but a man.