Stalingrad was an important target as it was Russia’s centre of communications in the south as well as being a centre for manufacturing. Stalin’s order was "Not a step backwards" Base on these, The Battle of Stalingrad was a cruel battle, Soviet Union and Germany were both suffered heavy casualties, more than 2 million people died. http://www.historylearningsite.co.uk/battle_of_stalingrad.htm
the british expeditionary force and french were unable to halt the German advance, they decided to evauate from northern France. over 332,226 men were rescued from Dunkirk, but most of heavy equitment was left.