Why was the United Nations formed?
It was formed in the aftermath and as a consequence of World War 2. It's aim was to prevent further conflicts and improve the rights and well being of everyone through its various structures.
The predecessor of the UN was The League of Nations. It was set up after World War 1. It's aim was to secure peace through international cooperation.
However the League repeatedly failed to achieve this objective. For example it was powerless to stop the German occupation of the Rhineland or the Japanese occupation of Manchuria.
The main problem was the USA never became a member.
When the UN was set up these issues were reflected in its structure. For example, the Security Council had 5 permanent members including the USA and Soviet Union. They had the power of veto recognising the fact that the support of the superpowers was essential for any action to be effective.
The General Assembly was the debating chamber where every member had equal status. It's numbers have more than trebled since World War 2reflecting the massive changes which have taken place because of decolonisation.
The UN also inherited the mandated territories of the League of Nations such as South Wesr Africa (Namibia) and Palestine. These proved very problematic.
The UN also established the Universal Declaration of Human Rights to ensure every individual had the right to experience basic human rights.
The Specialised Agencies such as WHO and UNESCO were established to tackle specific problems such as health and education. Their remit expanded rapidly as the European empires disintegrated and the number of countries in the exit 30 years trebled.