See how to file quarterly IFTA tax returns in Washington and get copies of your returns. File IFTA tax returns.Interstate and international agreement—Cooperation. International agreements are formal understandings or commitments between two or more countries. An agreement between two countries is called "bilateral," To promote international cooperation in teaching, research and other fields of mutual interest, the UW has formal partnerships with many non-U. United States and in international law. Culminating in January 1966 in a draft convention, complete with an elaborate commentary. International environmental agreements (IEAs) are signed treaties that regulate or manage human impact on the environment in an effort to protect it. Agreements between countries can be called treaties, agreements, conventions, and protocols.