The main allied powers during the World War II were Great Britain, The United States of America, China and the Soviet Union.
Step-by-step explanation:
The leaders of the Allies were Winston Churchill (Great Britain), Franklin Roosevelt (the United States),and Joseph Stalin (the Soviet Union).
The allies formed a defence against the attacks of axis powers.
When Germany invaded Poland, Great Britain and France declared war on Germany.
In May 1939, just a few months before Germany invaded Poland, they formalized their alliance with the Pact of Steel, a military and defensive agreement.