Answer:
Step-by-step explanation:
The first two paragraphs are a summary of fact. The tone is cool and collective. It puts in simple language that a threat, up until the Cuban Missel Crisis, was treated with respect and cool heads prevailed.
But once the soviets were seen as instigators of a policy that clearly violated the Monroe and later the Truman doctrines (though this was not stated), the tone changed and Kennedy's anger and steadfast determination to meat the challenge came out. Much is going on in that last stanza. Kennedy is warning the Soviet Union not to go to far. Their action will not be ignored and it will not be let slide under the rug. He will meet force with force if need be.
His tone is still calm, but he is both angry and determined.