The World War II (1939-1945):
It was almost six years and it was more aggressive. There was more killings and more consequences more than World War I. basically, the major forces were Germany (Hitler), Italy (Mussolini) and Japan. Poland, Britain and France were against Germany. The most threatening force was the Germans. The first date of World War II was when Germany attacked Poland. And already Poland, Britain and France had a treaty to protect each other because they knew that Germany would attack. Commonwealth= the colonies of the British whether it is an ex-colony or an existing colony. They call them the countries of the commonwealth. They used to belong to Britain or some of them were still colonies of Britain. The United Nations began in 1945 when the World War II ended.
So, a lot of results and consequences came out of these wars, especially, World War II. You have the expansion of the Soviet Union. It used to be Russia and then it became the Soviet Union. It expanded and it became a dominant power. Later on it demolished to a smaller countries. But after the World War II, it became a dominant power. You have the communists in China. All of these formed the United Nations as protecting the rights of countries.
(You have more details in the book)