A formal written agreement between two or more nations is commonly known as a treaty. A treaty is a legally binding agreement that is negotiated between two or more countries. The purpose of a treaty is to establish and regulate relationships between nations, resolve disputes, and promote cooperation on various issues such as trade, environment, human rights, and security.

The process of negotiating a treaty involves several stages, including the initial proposal, consultations, and formal negotiations. Once the terms of the treaty are agreed upon, it is then presented to each country`s respective government for approval. In most cases, a treaty is ratified by both countries` legislative bodies, such as the senate or parliament.

Treaties can take many different forms, depending on the nature of the agreement and the countries involved. Some of the most common types of treaties include bilateral treaties, which are signed between two countries, and multilateral treaties, which involve three or more countries.

One of the most famous multilateral treaties is the United Nations Charter, which was signed in 1945 by 51 countries at the end of World War II. The UN Charter established the United Nations, an international organization dedicated to promoting peace, cooperation, and human rights around the world.

Other notable treaties include the Geneva Conventions, which regulate the treatment of prisoners of war and civilians during times of armed conflict, and the Paris Agreement, which was signed by 196 countries in 2015 to address the issue of climate change.

Treaties can have a significant impact on the relationships between nations and the global community as a whole. They provide a framework for countries to work together on common goals and can help to prevent and resolve conflicts. However, treaties are only effective if they are enforced and respected by all parties involved.

In conclusion, a formal written agreement between two or more nations is called a treaty. Treaties are legally binding agreements that establish and regulate relationships between countries. They can take many different forms and have a significant impact on global cooperation and security.