I agree with Uncle_Sam. Furthermore, to think that the United Kingdom could have defeated Germany alone is not only a highly improbable hypothesis, but also one that is ridiculous. Without American intervention or assistance, Nazis flags might be decorating the city of London today. If you think about this question, the United Kingdom did fight the German alone [at least initially] and with very little success. To illustrate this fact, let’s just examine the state of affairs before America entered the conflict. And if we do this, we will have our answer – “NO WAY!” Let’s visit the summer of 1940. At that time, Hitler dominated Europe from the North Cape to the Pyrenees. His one remaining active enemy—Britain, under a new prime minister, Winston Churchill—vowed to continue fighting. The British army had left most of its weapons on the beaches at Dunker. Stalin was in no mood to challenge Hitler. The U.S., shocked by the fall of France, began the first peacetime conscription in its history and greatly increased its military budget, but public opinion, although sympathetic to Britain, was against getting into the war. The Germans hoped to subdue the British by starving them out. In June 1940 they undertook the Battle of the Atlantic, using submarine warfare to cut the British overseas lifelines. The Germans now had submarine bases in Norway and France. At the outset the Germans had only 28 submarines, but more were being built—enough to keep Britain in danger until the American entered the war to carry on the battle for months thereafter. Invasion was the expeditious way to finish off Britain, but that meant crossing the English Channel; Hitler would not risk it unless the British air force could be neutralized first. As a result, the Battle of Britain was fought in the air, not on the beaches. In August 1940 the Germans launched daylight raids against ports and airfields and in September against inland cities. The objective was to draw out the British fighters and destroy them. The Germans failed to reckon with a new device, radar, which greatly increased the British fighters' effectiveness. Because their own losses were too high the Germans had to switch to night bombing at the end of September. Between then and May 1941 they made 71 major raids on London and 56 on other cities, but the damage they wrought was too indiscriminate to be militarily decisive. On September 17, 1940, Hitler postponed the invasion indefinitely since the British were really in no position to invade Germany, thereby conceding defeat in the Battle of Britain. However, conceding defeat in this manner certainly did not make the British victorious. In short Great Britain declared war on Germany following the latter's invasion of Poland in 1939. After withdrawing her expeditionary force from France in June 1940, she continued the war on other fronts, chiefly by the long-drawn-out Battle of the Atlantic against the German submarine menace and the seesaw battles against the German Afrika Corps in the Western Desert of North Africa making little significant strategic inroads. It was not until the joint Anglo-American invasions of Italy and the final D-Day invasion of Nazi-held Europe that the Third Reich started to crumble.