“But when she discarded the yoke of Versailles, Germany started from scratch, as it were. She initiated the development of a complete armament program, closely integrated with civil industry. Had the great nations grown old together in the gradual elimination of outmoded weapons, planes and equipment, no single nations could have gained so long a lead as Germany has. Contradictory as it may seem, Germany actually profited by the wiping out of her World War armament.”
As to how Marshall's observation was applied, there wasn't much he could do about it in 1939. How much influence did he have in 1945 when the post-war occupations and rebuilding took place? Germany and Japan haven't started any wars since.