While the development of tanks had largely led to the replacement of cavalry in most armies by 1939, the Soviets retained a strong mounted arm. In the terrain and conditions of the Eastern Front they were able to play an important role denied them elsewhere. John Harrel shows how the Soviets developed a doctrine of deep penetration, using cavalry formations to strike into the Axis rear, disrupting logistics and lines of communication, encircling and isolating units. Interestingly he shows that this doctrine did not stem from the native cavalry tradition of the steppe but from the example of the American Civil War. The American approach was copied by the Russians in WWI and the Russian Civil War, refined by the Soviets in the early stages of World War Two and perfected during the last two years of the war. The Soviet experience demonstrated that deep operations (cavalry raids) against enemy rear echelons set the conditions for victory. Although the last horse-mounted units disappeared in the 1950s, their influence led directly to the formation of the Operational Manoeuvre Groups that, ironically, faced US forces in the Cold War.

The war of 337-363 (which the author dubs the Nisibis War), was an exception to the traditional Roman reliance on a strategic offensive to bring about a decisive battle. Instead, the Emperor Constantius II adopted a defensive strategy and conducted a mobile defence based upon small frontier (limitanei) forces defending fortified cities, supported by limited counteroffensives by the Field Army of the East. These methods successfully checked Persian assaults for 24 years. However, when Julian became emperor his access to greater resources tempted him to abandon mobile defence in favour of a major invasion aimed at regime change in Persia. Although he reached the Persian capital, Ctesiphon, he failed to take it, was decisively defeated in battle and killed. The Romans subsequently resumed and refined the mobile defence, allowing the Eastern provinces to survive the fall of the Western Empire. John Harrel applies his personal experience of military command to a strategic, operational, tactical and logistical analysis of these campaigns and battles, highlighting their long-term significance.