The original Allies during the war were Great Britain, Poland, and France. That meant that these three countries were friends who would help each other out if necessary. When Germany invaded Poland in 1939, Britain and France rushed to its aid and declared war.
With Britain came its territories of Canada, Australia, New Zealand, and South Africa.
By 1941, the first Allies were joined by even more friends from the countries of Belgium, Brazil, China, Denmark, Norway, India, Greece, the Netherlands, Soviet Union and finally the United States. That’s a lot of friends!
The Allies eventually became the United Nations we know today.