Of the military and historical lessons presented by the Great War, the necessity for military cooperation between sovereign allies is paramount. Because of the universal distaste for this war and the suffering which it brought, historians have been slow in perceiving the true character of the cooperative military operations conducted by the Entente Powers in the period 1914-1918. Field-Marshal Sir Douglas Haig, the commander of the British Armies in France, served with or under all four of France's high commanders during the war. Despite his understandable sensitivity to excessive French domination, he was more than cooperative with all of these men and, in many instances, submerged his personal desires in order to maintain a semblance of unity in joint military action on the Western Front. The immense influence -- both positive and negative -- which Haig exercised over the schemes for cooperative action has been largely overlooked or unappreciated by intervening analysts. There can be little doubt that Field-Marshal Haig was the single most important commander in the Allied coalition during the final two years of the war. His armies prevented the Germans from destroying the French at Verdun and distracted the German High Command from the utter helplessness of the French during the Army mutinies of 1917. In the final months of the war, while the fledgling American Army was being brought into the line, the British blunted the German last gamble offensives. Following this, Haig led his force to decisively defeat the principal enemy in the only theater of operations where final victory could be achieved, the Western Front. During his period of command, Haig accepted a subordinate role to Joffre and Nivelle. During Petain's tenure as Commander-in-Chief, he worked as an honest partner to relieve pressure from the hard-pressed French. Haig successfully thwarted the attempts of the Allied political leaders to impose direction by a committee upon the military commanders. When imminent disaster confronted the alliance, Haig finally accepted formal subordination under the Generalissimo, Foch. Although the results of Haig's cooperative efforts were appreciated by the Allies during the Second World War, the techniques used to achieve this goal were never fully understood.