The Doctrine called Communism "the world's foremost evil" and stated the "United States can not - and will not - sit by as this evil consumes more and more lives of the innocent." Simply, the Doctrine stated that Communism was a form of oppression of free people, and all free nations ought to fight against this oppression. The MacArthur Doctrine was also later invoked when MacArthur and his State Department led to a major push to authorize and establish the Asia-Pacific Treaty Organization.