Local successes on the _field of battle_ often have effects that are felt throughout the _theatre of operations_. Lord Roberts's advance on Pretoria relieved the pressure on Kimberley in the west and on Ladysmith in the east, and these centres are upwards of 300 miles apart. _The {7} First Battle of the Somme_ (July 1, 1916) not only relieved the pressure on Verdun but held in position large enemy forces which would otherwise have been employed against our Allies in the East. General Byng's surprise attack at Cambrai (November 20, 1917) was followed by a determined counter-attack by the Germans on November 30, which appeared to nullify the results achieved from November 20 to 25; but "there is evidence that German divisions intended for the Italian theatre were diverted to the Cambrai front, and it is probable that the further concentration of German forces against Italy was suspended for at least two weeks at a most critical period, when our Allies were making their first stand on the Piave Line" (Sir D. Haig's Dispatches). A tactical defeat may sometimes be risked to serve a strategic end. In June, 1864, General Hunter was operating with a Federal army in the Shenandoah Valley, and owing to shortage of supplies was forced to fall back. In so doing he uncovered the National Capital, and General Early was sent by the Confederate Commander-in-Chief to capture Washington. General Grant took immediate steps to protect the capital by the dispatch of troops, and to further this end, General Lew Wallace,[1] on his own initiative, confronted Early's corps at the _Monocacy_ on July 8, 1864. He met the enemy and was defeated, but he delayed Early's corps until the troops sent by Grant were in position. "If Early had been but one day _earlier_ he might have entered the capital before the arrival of the reinforcements I had sent. General Wallace contributed on this occasion, by the defeat of the troops under him, a greater benefit to the cause than often falls to the lot of a commander of an equal force to render by means of a victory" (Grant's "Memoirs"). A tactical success may be not only useless, but actually inopportune, if it is out of accord with the plans of the higher command. On the morning of June 18, 1815, Marshal Grouchy was in {8} pursuit of the Prussians whom Napoleon had defeated on June 16 at Ligny. Although urged "to march to the sound of the cannon" (at Waterloo), Grouchy pushed on eastwards, where he found Thielmann's Prussian Corps of 16,000 men holding the passage across the Dyle at Wavre. The _Battle of Wavre_ was begun at 4 p.m. on June 18, and by 11 a.m. on the next day Grouchy was victorious. But his victory was barren. His tactical achievement was useless to the higher command and had exposed his own force to considerable danger. As he sat down to pen a vainglorious dispatch to the Emperor, he received the news that Napoleon was a fugitive and the Imperial Army defeated and scattered. Grouchy's