The ____________ was the first Intergovernmental Organisation that tried to maintain peace across the world.

Commonwealth
Navigation of the Rhine
United Nations
None of the above

League of Nations

The first Intergovernmental Organisation that tried to maintain peace across the world was the "League of Nations."

To find the answer to this question, we can eliminate each option and see which one is correct.

- The Commonwealth is an intergovernmental organization comprising 54 member countries, primarily former territories of the British Empire. However, it is primarily focused on fostering cooperation and development among its member states, rather than maintaining peace across the world. Therefore, the Commonwealth is not the correct answer.

- The Navigation of the Rhine is a treaty that regulates navigation and commerce on the Rhine River in Europe. While it is an intergovernmental agreement, its scope is limited to the navigation of the Rhine River, and it does not aim to maintain peace across the world. Therefore, the Navigation of the Rhine is not the correct answer.

- The United Nations (UN) is an intergovernmental organization founded in 1945 after World War II. Its main purpose is to maintain international peace and security, and it has taken various measures throughout its existence to promote peace and resolve conflicts worldwide. Therefore, the United Nations is the correct answer.

Thus, the correct answer is the United Nations.