Most Americans know the Japanese attack on Pearl Harbor 70 years ago was a turning point in World War II, finally drawing the United States into the conflict. Winston Churchill's reaction is revealing: "So we have won after all." That night, he later wrote, he "went to bed and slept the sleep of the saved and thankful."

What few know is that another, almost simultaneous battle halfway around the world can be seen as equally decisive in the outcome of the war. On the night of Dec. 5-6, 1941, with Hitler's forces just 12.5 miles from Moscow, a Russian counterattack drove the Germans back 100 miles, ending any chance that the blitzkrieg would succeed. With America's attention understandably focused on the Pacific, few of its citizens understood the significance of the German setback, which Hitler largely brought on himself.

The German campaign against the Soviet Union, Operation Barbarossa, began on June 22, 1941. It targeted three areas: Leningrad in the north, Moscow in the center, and Ukraine in the south. Emboldened by his successful conquest of Poland, Norway, Denmark, Belgium, Holland, and France, Hitler expected a quick victory. The Germans had only to "kick in the door and the whole rotten edifice will collapse," he predicted.

For the first two months, he appeared to be right. Russian defenses collapsed; huge armies were surrounded and surrendered as German armored strikes cut deeper into the Soviet Union. And then Hitler made a fatal decision that eventually cost him the campaign, setting the stage for Germany's ultimate defeat.

Until then, Hitler had only rarely intervened in strategic or tactical planning. But in mid-August, he ordered a deviation from the original war plan. Against the wishes of his generals, who wanted to strike directly for Moscow, Hitler ordered a diversion of forces, especially valuable armored units, to try to secure the vast oil fields of the Caucasus region to the south.

For six weeks, fighting stalled around Moscow. Finally, on Oct. 2, with the German press proclaiming victory, Hitler ordered a major offensive on the city. But it proved too late.

The freezing rain that had begun in late September had by early October turned the region's roads into mud and slush. Then the temperatures began to fall, reaching 30 below zero in some places as the Germans struggled to surround Moscow.

The vaunted German war machine ground to a halt. Freezing temperatures made it impossible to start tank and truck engines as motor oil reached the viscosity of tar. Sophisticated German artillery weapons were also rendered useless.

More significantly, Stalin began to move fresh troops - nearly 100 divisions - from the Far East, where they had been guarding against attack from Japan, with which Russia had fought an undeclared war in 1938-39. Stalin did so because his master spy in Tokyo, Richard Sorge, had informed him that the Japanese were going to strike south against the Americans, not north into Siberia.

The added divisions sealed the German army's fate before it reached Moscow. It suffered more than 900,000 casualties, losing almost 30 percent of the troops committed to the campaign.

Combined with Hitler's failure to defeat the Soviets, the Japanese attack on the United States established the parameters of the rest of the war. Despite their success at Pearl Harbor and in the South Pacific over the next six months, the Japanese failed to break America's will. By mid-1942, the United States was on the offensive at Midway and Guadalcanal. At the same time, the Germans had made an enemy of America without dispatching the Soviet Union - a major miscalculation on Hitler's part.

It can be argued that once they failed to destroy their main enemies in a single campaign, Germany and Japan could no longer win. And so two battles, halfway around the world from each other, determined the direction of the war.