What happened at Dunkirk in May 1940?

What happened at Dunkirk (France) in 1940 was the
evacuation of the British Expeditionary Force (and a fairly large number of French and
other continental European soldiers to England.  This evacuation was hugely important
because it allowed the British army to continue being a part of the war and it allowed
for the creation of a "Free French" force.

In the spring of
1940, the Germans had swept across Western Europe in the "blitzkrieg."  The British
Expeditionary Force and the French Army had been unable to do much to resist.  By late
May, the remnants of these forces were trapped in Dunkirk.  If the Germans had either
killed or captured these people, the war might well have been
over.

However, the British were able to evacuate 338,000
soldiers from Dunkirk.  This was one of the most significant events of
WWII.