It was in Moltke's "Instructions for Large Unit Commanders" and his concept of separated armies that we begin to see the emergence of modern German doctrine. The system of moving units separately and concentrating as an army before a battle resulted in more efficient supply and lower vulnerability to modern firepower. To enable a successful flanking attack, he asserted that concentration could only take place after the commencement of a battle. This was a development of the Scharnhorst concept of "March Divided, Fight United."