Why was the German arrival at Abbeville on May 20 important?

The German arrival at Abbeville on May 20, 1940, was a critical turning point in the Battle of France because it effectively severed all communications and physical links between the Allied forces stationed in the north and those in the south.12

By reaching the mouth of the Somme River at the English Channel, German armored forces—led by Gen. Heinz Guderian—completed a strategic maneuver that trapped the British Expeditionary Force, the Belgian army, and several French armies in the north. This maneuver isolated these massive Allied formations, leaving them vulnerable and setting the stage for the subsequent German drive north toward the Channel ports of Calais and Dunkirk, which were the last remaining escape routes for the British.123