The Allied strategy in Europe in World War II had a number of parts. Basically, the strategy was to engage in strategic bombing of Germany until it was possible to invade. In the meantime, the Soviets continued to fight Germany.
For much of the war, only the USSR was engaging in major land combat with Germany. During that time, the Western Allies engaged in strategic bombing to reduce the German war capacity. Eventually, they opened second fronts, beginning with the invasion of Italy and culminating with the D-Day invasions. This relieved some pressure on the Soviets and ended up defeating Germany.