Basically, President Truman's plan in using the atomic bombs was to impress and effectively scare the Soviet Union into stopping their expansion into Asia.
Humble leaders use their expertise, experience and knowledge to bring together people to increase revenue, improve production or efficiency and return to the community. Leaders who are modest use their successes for the common good than for self-extension.
Austria-hungary and Serbia were the first two nations. However, I do not know much about why the americans joined the war. Sorry.
Answer:
The cartoon is meant as a symbol that stands for strength in numbers, meaning that the colonies would be stronger if they all worked together. The pieces of the snake are representing the colonies.