Please, look at the first part.
The Second Phase: Expansion of the War
In the year after the fall of France, the war moved toward a new stage—world war. While conducting subsidiary campaigns in the Balkans, in North Africa, and in the air against Britain, Hitler deployed his main forces to the east and brought the countries of southeastern Europe (as well as Finland) into a partnership against the USSR.
U.S. Aid to Britain
The United States abandoned strict neutrality in the European war and approached a confrontation with Japan in Asia and the Pacific Ocean. U.S. and British conferences, begun in January 1941, determined a basic strategy for the event of a U.S. entry into the war, namely, that both would center their effort on Germany, leaving Japan, if need be, to be dealt with later. In March 1941 the U.S. Congress passed the Lend-Lease Act and appropriated an initial $7 billion to lend or lease weapons and other aid to any countries the president might designate. By this means the United States hoped to ensure victory over the Axis without involving its own troops. By late summer of 1941, however, the United States was in a state of undeclared war with Germany. In July, U.S. Marines were stationed in Iceland, which had been occupied by the British in May 1940, and thereafter the U.S. Navy took over the task of escorting convoys in the waters west of Iceland. In September President Franklin D. Roosevelt authorized ships on convoy duty to attack Axis war vessels.
Friction Between the U.S. and Japan
Meanwhile, American relations with Japan continued to deteriorate. In September 1940 Japan coerced Vichy France into giving up northern Indochina. The United States retaliated by prohibiting the exportation of steel, scrap iron, and aviation gasoline to Japan. In April 1941, the Japanese signed a neutrality treaty with the USSR as insurance against an attack from that direction if they were to come into conflict with Britain or the United States while taking a bigger bite out of Southeast Asia. When Germany invaded the USSR in June, Japanese leaders considered breaking the treaty and joining in from the east, but, making one of the most fateful decisions of the war, they chose instead to intensify their push to the southeast. On July 23 Japan occupied southern Indochina. Two days later, the United States, Britain, and the Netherlands froze Japanese assets. The effect was to prevent Japan from purchasing oil, which would, in time, cripple its army and make its navy and air force completely useless.
The German Invasion of the USSR
The war’s most massive encounter, dubbed Operation Barbarossa, began on the morning of June 22, 1941, when slightly more than 3 million German troops invaded the USSR. Although German preparations had been visible for months and had been talked about openly among the diplomats in Moscow, the Soviet forces were taken by surprise. Stalin, his confidence in the country’s military capability shaken by the Finnish war, had refused to allow any counteractivity for fear of provoking the Germans. Moreover, the Soviet military leadership had concluded that blitzkrieg, as it had been practiced in Poland and France, would not be possible on the scale of a Soviet-German war; both sides would therefore confine themselves for the first several weeks at least to sparring along the frontier. The Soviet army had 2.9 million troops on the western border and outnumbered the Germans by two to one in tanks and by two or three to one in aircraft. Many of its tanks and aircraft were older types, but some of the tanks, particularly the later famous T-34s, were far superior to any the Germans had. Large numbers of the aircraft were destroyed on the ground in the first day, however, and their tanks, like those of the French, were scattered among the infantry, where they could not be effective against the German panzer groups. The infantry was first ordered to counterattack, which was impossible, and then forbidden to retreat, which ensured their wholesale destruction or capture.
Initial German Successes
For the invasion, the Germans had set up three army groups, designated as North, Center, and South, and aimed toward Leningrad, Moscow, and Kyiv. Hitler and his generals had agreed that their main strategic problem was to lock the Soviet army in battle and defeat it before it could escape into the depths of the country. They disagreed on how that could best be accomplished. Most of the generals believed that the Soviet regime would sacrifice everything to defend Moscow, the capital, the hub of the road and railroad networks, and the country’s main industrial center. To Hitler, the land and resources of the Ukraine and the oil of the Caucasus were more important, and he wanted to seize Leningrad as well. The result had been a compromise—the three thrusts, with the one by Army Group Center toward Moscow the strongest—that temporarily satisfied Hitler as well as the generals. War games had indicated a victory in about ten weeks, which was significant because the Russian summer, the ideal time for fighting in the USSR, was short, and the Balkans operations had caused a 3-week delay at the outset. Ten weeks seemed ample time. Churchill offered the USSR an alliance, and Roosevelt promised lend-lease aid, but after the first few days, their staffs believed everything would be over in a month or so. By the end of the first week in July, Army Group Center had taken 290,000 prisoners in encirclements at Białystok and Minsk. On August 5, having crossed the Dnieper River, the last natural barrier west of Moscow, the army group wiped out a pocket near Smolensk and counted another 300,000 prisoners. On reaching Smolensk, it had covered more than two-thirds of the distance to Moscow.
Hitler’s Change of Plan
The Russians were doing exactly what the German generals had wanted, sacrificing enormous numbers of troops and weapons to defend Moscow. Hitler, however, was not satisfied, and over the generals’ protests, he ordered Army Group Center to divert the bulk of its armor to the north and south to help the other two army groups, thereby stopping the advance toward Moscow. On September 8 Army Group North cut Leningrad’s land connections and, together with the Finnish army on the north, brought the city under siege. On September 16 Army Group South closed a gigantic encirclement east of Kyiv that brought in 665,000 prisoners. Hitler then decided to resume the advance toward Moscow and ordered the armor be returned to Army Group Center. See also Leningrad, Siege of.
The Attempt to Take Moscow
After a standstill of six weeks, Army Group Center resumed action on October 2. Within two weeks, it completed three large encirclements and took 663,000 prisoners. Then the fall rains set in, turning the unpaved Russian roads to mud and stopping the advance for the better part of a month. In mid-November, the weather turned cold and the ground froze. Hitler and the commander of Army Group Center, Field Marshal Fedor von Bock, faced the choice of having the armies dig in where they were or sending them ahead, possibly to be overtaken by the winter. Wanting to finish the 1941 campaign with some sort of a victory at Moscow, they chose to move ahead. In the second half of November Bock aimed two armored spearheads at Moscow. Just after the turn of the month, one of those, bearing in on the city from the northwest, was less than 32 km (less than 20 mi) away. The other, coming from the south, had about 65 km (about 40 mi) still to go. The panzer divisions had often covered such distances in less than a day, but the temperature was falling, snow was drifting on the roads, and neither the men nor the machines were outfitted for extreme cold. On December 5 the generals commanding the spearhead armies reported that they were stopped: The tanks and trucks were freezing up, and the troops were losing their will to fight.
Soviet Counteroffensive
Stalin, who had stayed in Moscow, and his commander at the front, General Georgy Zhukov, had held back their reserves. Many of them were recent recruits, but some were hardened veterans from Siberia. All were dressed for winter. On December 6 they counterattacked, and within a few days, the German spearheads were rolling back and abandoning large numbers of vehicles and weapons, rendered useless by the cold. On Stalin’s orders, the Moscow counterattack was quickly converted into a counteroffensive on the entire front. The Germans had not built any defense lines to the rear and could not dig in because the ground was frozen hard as concrete. Some of the generals recommended retreating to Poland, but on December 18 Hitler ordered the troops to stand fast wherever they were. Thereafter, the Russians chopped great chunks out of the German front, but enough of it survived the winter to maintain the siege of Leningrad, continue the threat to Moscow, and keep the western Ukraine in German hands. See also Battle of Moscow.
The Beginning of the War in the Pacific
The seeming imminence of a Soviet defeat in the summer and fall of 1941 had created dilemmas for Japan and the United States. The Japanese thought they then had the best opportunity to seize the petroleum and other resources of Southeast Asia and the adjacent islands; on the other hand, they knew they could not win the war with the United States that would probably ensue. The U.S. government wanted to stop Japanese expansion but doubted whether the American people would be willing to go to war to do so. Moreover, the United States did not want to get embroiled in a war with Japan while it faced the ghastly possibility of being alone in the world with a triumphant Germany. After the oil embargo, the Japanese, also under the pressure of time, resolved to move in Southeast Asia and the nearby islands. See also War in the Pacific.
Pearl Harbor
Until December 1941 the Japanese leadership pursued two courses: They tried to get the oil embargo lifted on terms that would still let them take the territory they wanted, and they prepared for war. The United States demanded that Japan withdraw from China and Indochina, but would very likely have settled for a token withdrawal and a promise not to take more territory. After he became Japan’s premier in mid-October, General Tōjō Hideki set November 29 as the last day on which Japan would accept a settlement without war. Tōjō’s deadline, which was kept secret, meant that war was practically certain. The Japanese army and navy had, in fact, devised a war plan in which they had great confidence. They proposed to make fast sweeps into Burma, Malaya, the East Indies, and the Philippines and, at the same time, set up a defensive perimeter in the central and southwest Pacific. They expected the United States to declare war but not to be willing to fight long or hard enough to win. Their greatest concern was the U.S. Pacific Fleet, based at Pearl Harbor, Hawaii. If it reacted quickly, it could scramble their very tight timetable. As insurance, the Japanese navy undertook to cripple the Pacific Fleet by a surprise air attack.
A few minutes before 8 AM on Sunday, December 7, 1941, Japanese carrier-based airplanes struck Pearl Harbor. In a raid lasting less than two hours, they sank or seriously damaged eight battleships and 13 other naval vessels. The U.S. authorities had broken the Japanese diplomatic code and knew an attack was imminent. A warning had been sent from Washington, but, owing to delays in transmission, it arrived after the raid had begun. In one stroke, the Japanese navy scored a brilliant success—and assured the Axis defeat in World War II. The Japanese attack brought the United States into the war on December 8—and brought it in determined to fight to the finish. Germany and Italy declared war on the United States on December 11.
Japanese Conquests in Asia and the Pacific
In the vast area of land and ocean they had marked for conquest, the Japanese seemed to be everywhere at once. Before the end of December, they took British Hong Kong and the Gilbert Islands (now Kiribati) and Guam and Wake Island (U.S. possessions), and they had invaded British Burma, Malaya, Borneo, and the American-held Philippines. British Singapore, long regarded as one of the world’s strongest fortresses, fell to them in February 1942, and in March they occupied the Netherlands East Indies and landed on New Guinea. The American and Philippine forces surrendered at Bataan on April 9, and resistance in the Philippines ended with the surrender of Corregidor on May 6.
According to the Japanese plan, it would be time for them to take a defensive stance when they had captured northern New Guinea (an Australian possession), the Bismarck Archipelago, the Gilberts, and Wake Island, which they did by mid-March. But they had done so well that they decided to expand their defensive perimeter north into the Aleutian Islands, east to Midway Island, and south through the Solomon Islands and southern New Guinea. Their first move was by sea, to take Port Moresby on the southeastern tip of New Guinea. The Americans, using their ability to read the Japanese code, had a naval task force on the scene. In the ensuing Battle of the Coral Sea (May 7-8), fought entirely by aircraft carriers, the Japanese were forced to abandon their designs on Port Moresby.
The Battle of Midway
A powerful Japanese force, nine battleships and four carriers under Admiral Yamamoto Isoroku, the commander in chief of the navy, steamed toward Midway in the first week of June. Admiral Chester W. Nimitz, who had taken command of the Pacific Fleet after Pearl Harbor, could only muster three carriers and seven heavy cruisers, but he was reading the Japanese radio messages. Yamamoto, the architect of the Pearl Harbor raid, had planned another surprise. This time, however, it was he who was surprised. Off Midway, on the morning of June 4, U.S. dive-bombers destroyed three of the Japanese carriers in one 5-minute strike. The fourth went down later in the day, after its planes had battered the U.S. carrier Yorktown, which sank two days later. See Midway, Battle of.
Yamamoto ordered a general retreat on June 5. On June 6-7 a secondary Japanese force took Kiska and Attu in the Aleutians, but those were no recompense for the defeat at Midway, from which the Japanese navy would never recover. Their battleships were intact, but the Coral Sea and Midway had shown carriers to be the true capital ships of the war, and four of those were gone.
