The German advance in the Soviet Union came to a halt on the outskirts of Moscow in October 1941. When the autumn set in, the tanks got stuck in the mud due to the rain. Before long, it was winter.
It was the coldest winter in decades. It was so cold that many vehicles stopped working. Since the German army command had counted on a quick victory, the soldiers did not have proper winter clothes, and they suffered from the cold. The cold was not the only problem, though. Moscow was so far away from Germany, that it was very difficult to supply the troops with weapons and food.