Answer: They knew they had to unite to avoid defeat.
Explanation:
The Axis powers of Germany, Italy and Japan swept across the world in the second World War and with overwhelming strength and tactics, overwhelmed many areas that were not supposed to have fallen so easily.
In Europe for instance, the Germans crushed the British and French armies such that France was defeated and occupied in a month and the British had to be evacuated frantically. Germany then went on to conquer most of Europe and began attacking Africa. When they launched an attack into the Soviet Union, they almost captured Moscow.
In Asia, Japan swept across the islands and nations of east Asia and captured massive territories in China as well as capturing the Philippians and Indonesia. They also attacked Hawaii in a bid to destroy the U.S. Pacific fleet.
When the allies saw the massive Axis war machine and power that faced them, they knew they had to unite to stand a chance of winning. This led to the Communist Soviet Union and the Western powers of Britain and the U.S. uniting against the Axis even though they did not trust one another.
