Answer:
Hello!
The United Nations (UN) were created after the end of WW2 after the league of nations couldn't stop world war 2 from happening.
Once established they tried to create a world order and peace balance after the war with multiple leaders of countries coming out to meet and discuss.
Over time the UN established multiple branches some examples being, The Security Council, and The Economic and Social council.
They assisted both superpowers during the cold war as tension rised between both of them.
And the bigger the UN got the more leaders and representatives of countries joined the UN including, the Middle East, Asia, Africa, Etc.
Step-by-step explanation:
This is a pretty short but basic summary of some ways they evolved in the twentieth century i hoped this helped!