Final answer:
The term 'United Nations' was coined by United States President Franklin D. Roosevelt during World War II and led to the founding of the UN in 1945.
Step-by-step explanation:
The name 'United Nations,' coined by United States President Franklin D. Roosevelt, was first used in the Declaration by United Nations of 1 January 1942, during the Second World War. Representatives of 26 nations pledged their governments to continue fighting together against the Axis Powers. After the war, the United Nations was established as an international organization in 1945, with 51 member states, to ensure global peace and security, which was a significant step following the shortcomings of the League of Nations after World War I.