"i believe that it must be the policy of the united states to support free peoples who are resisting attempted subjugation by armed minorities or by outside we falter in our leadership, we may endanger the peace of the world - and we shall surely endanger the welfare of our own nation" -president harry truman, 1947 what threat was president truman referring to in the excerpt above?

The threat of Soviet and communist aggression.

Context/details:

The statement was a part of what became known as "The Truman Doctrine."  The policy was first stated by President Truman in an address to Congress in 1947, when he said, "It must be the policy of the United States to support free people who are resisting attempted subjugation by armed minorities or by outside pressures."  Essentially, the Truman Doctrine pledged American effort elsewhere in the world to check the spread of communist and Soviet influence.  The policy was first put into action in 1948 by providing economic support to Greece and Turkey to stave off communist movement in those countries.  The essence of this policy was called "containment" -- keeping communism where it was and stopping it from spreading.  

The containment policy had been recommended by George F. Kennan, America's ambassador in Moscow after World War II.  In 1946, he sent what became known as "the long telegram" of his advice about what the USA needed to do about the Union of Soviet Socialist Republics (USSR).  Kennan took note of the internal problems the USSR had.  He advised not pushing the conflict too much, but instead just try to "contain" the Soviet Union rather than going to battle against the USSR directly.

what was the significance of the plessy vs ferguson ruling and jim crow laws

answer the impact. plessy v. ferguson allowed 'separate but equal, also known as segregation, to become law in the united states