Complex sentence: When war was declared in 1939 Gamelin was France's commander in chief and saw little action during the Phoney War, save a few French divisions crossing the German border in the Saar Offensive but only travelled a mere.
Split into simpler sentences: When war was declared in 1939, Gamelin was France's commander in chief. France saw little action during the Phoney War, save a few French divisions crossing the German border in the Saar Offensive who travelled a mere.