By the Spring of 1941 Great Britain had emerged from the threat of annihilation, but she had by no means gained the upper hand. When Mussolini invaded Greece in October 1940, Britain was unable to man a Balkan front. A British expeditionary force landed on the Greek mainland, but it was not strong enough to save the Greeks. When it was withdrawn to Africa, however, it was powerful enough to halt an Axis offensive. In April 1941 the Germans invaded Yugoslavia on the pretext that she had violated the 'Tripartite Pact', and then pressed on to relieve the Italians in Greece. The British were forced hastily to re-embark. A daring German parachute operation rooted them out of Crete. King George had no place to go but Cairo. Throughout the continent, the Germans expropriated what wealth and equipment they found. Belief in ultimate German victory induced many citizens in the occupied spates, including the Vichy Government, to 'collaborate' with the Germans. The imbalance between the two camps may not have increased in Britain's disfavour, but they continued to be unevenly matched. England had not won the war. No one knew how or when shewould. Prospects remained uncertain until 21 June 1941, when the Wehrmacht invaded Soviet Russia. The attack caught the Soviet heads of state, especially Stalin, by surprise. They had been careful to adhere to the letter ol the Russo-German Pact, while openly pursuing their own interests. At the same time, they had proceeded with territorial acquisition. They absorbed the Baltic states and Lithuania. They took part ol Bessarabia and Bukovina from Rumania, and they occupied part of Finland. These manoeuvres displeased Hitler, who had not abandoned the great plan flaunted in Mein Kampfof following the path ol the Teutonic Knights to colonize the vast plain inhabited by the Slavs, whom he regarded as inferiors. His plan also had the merit of annihilating the bolshevik heresy. The huge European force which Hitler hurled into his crusade comprised Finns, Hungarians, Slovaks, Rumanians, and Italians as well as volunteer contingents raised from occupied countries, including a few thousand Frenchmen. There were 205 divisions of infantry and 30 armoured divisions which marshalled 4,000 tanks. These ground forces were supported by 3,000 aircraft. Three groups of armies were pointed at three targets - Leningrad, Moscow and the Ukraine, which offered rich supplies of wheat and iron. It remained to be seen whether these troops were sufficient to occupy and hold the vast expanse of Soviet Russia. It appeared that they might be for the first six months. The Red Army was large but disquietingly weak and ill-prepared for modern warfare. Stalin's purges had decimated the high command. Tanks had not been organized in large units, while Soviet fighter planes were no faster than German bombers. Fortifications were also weak. The Wehrmacht advanced three hundred miles in eighteen days of fighting and by 2 September, Leningrad was within range of enemy fire. At Kiev, which fell on 25 September, 600,000 prisoners were taken. By 2 October Moscow was under attack. The Russians yielded but they did not give way. They provided for future contingencies by dismantling and transporting hundreds of factories and thousands of workers up to and across the Urals. They brought in reinforcements from Siberia and reorganized their high command, placing Zhukov in charge of Moscow defences. By winter, Leningrad was under siege but it did not capitulate. The Germans were forced back from Moscow. This, their last attempt at lightning war, did not bring them victory. It had become a war of attrition and appeared likely to drag on. By spring 1942, German offensive loi ces were still stronger than the Russian, but their manoevres were restricted to objectives along the Volga and in the' Caucasus. Again the Russians yielded, but they retreated inch by inch. They had learned how to wage war and they had new equipment. In addition, the German policy of systematic terror in the occupied territories discouraged collaboration and prevented the formation oi anti-Soviet splinter groups.