Complex sentence: Further north, Major-General Erwin Rommel also kept pushing on quickly, against commands from his superiors and so came to the sea to the West of the BEF trapping the forces that had been sent into the Low Countries around Arras and Dunkirk.
Split into simpler sentences: Further north, Major-General Erwin Rommel also kept advancing quickly, against the orders from his superiors. He reached the sea to the west of the BEF trapping the forces that had been sent into the Low Countries around Arras and Dunkirk.