What is a formal agreement between two or more sovereign states called?

A formal agreement between two or more sovereign states is termed a treaty. Treaties are legally binding agreements and are often negotiated between countries to manage various aspects of their relationships, including trade, peace, and mutual cooperation. The process for creating a treaty typically involves negotiation, signing, and ratification, reflecting the sovereign authority of the states involved.

In contrast, the other terms, while related to international agreements, do not carry the same formal legal status as treaties. For example, a protocol may refer to an amendment or an addition to an existing treaty or an agreement made within an international conference setting, but it does not inherently have the same weight as a treaty. An accord generally signifies a less formal agreement and may not always require the same ratification process. A convention is typically used to describe international agreements that establish frameworks or norms, often in longer-term contexts, but again, these may not possess the same binding nature as a treaty. Thus, the distinction lies in the level of formality and legal binding nature, making 'treaty' the correct choice.