1) The United States operates under a two-party system, with the Democratic Party and the Republican Party being the two major political parties that compete in elections and shape the country's political landscape.

2) International relations encompass the study of relationships between nations, including diplomacy, treaties, and foreign policy. It examines the interactions and dynamics among different countries in the global arena.

3) The Dead Sea, located between Jordan and Israel, is the lowest point on Earth's surface. Its saltwater is so dense that people can easily float on its surface.

4) The word "oxygen" contains two vowels: O and E.