In the lead-up to the Truman Doctrine.

The policy of containment was one of the most important policies the US developed. Not only did it suggest to actively seeking to prevent the spread of communism, but also it was also the key aim in "Truman Doctrine"--the Doctrine that veered the US's attitude towards the rest of the world. It said, "it was America's duty to interfere to 'help free peoples to work out their own destiny in their own way'", which abandoned the previous policy, the policy of isolation. How did the allies in the Second World War turn against each other and what caused the USA to abandon its long-term isolation…