But Stalin had decided to stay in Moscow and make a stand. Under a "state of siege," 500,000 men and women dug 5,000 miles of trenches around the city; equipment from 500 factories was shipped east to keep it out of Nazi hands. For the forthcoming battle, Stalin refused to allow his commanders to make tactical withdrawals. As Red Army soldiers dug into the fields on the outskirts of Moscow, new defense works were built directly behind the troops, manned by special units of the NKVD. These forces aimed their guns not at the Germans, but at soldiers of the Red Army who dared to retreat.
“We forced them to fight to the death. If they resisted or ran away we eliminated them. We shot them. That's all. They weren't fighters anymore. It was hard. It was bad. I understand. But what can you do?”- Vladimir Ogryzko, 1st NKVD Division
Weeks passed and the harsh Russian winter took a toll on the Germans, now fighting in blizzard conditions with snow waist-high. The Nazi advance stalled. On December 5, the Red Army counter-attacked in a blinding blizzard, forcing the Germans to retreat—in some places more than one hundred miles back from Moscow. It wasn't a total victory, but for the Soviets it was a cause for celebration.
On December 7, the Japanese bombed the United States fleet at Pearl Harbor; the United States immediately declared war on Japan. Four days later, Germany, Japan’s ally, also declared war on the United States. The world’s biggest economy was now in the war.