1) 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.

2) The Treaty of Tordesillas, signed in 1494, divided the newly discovered lands outside of Europe between Spain and Portugal, leading to the colonization of the Americas.

3) Pizza, a popular Italian dish, originated in Naples and is now enjoyed worldwide. Traditional Neapolitan pizza features a thin, chewy crust topped with San Marzano tomatoes, mozzarella cheese, and fresh basil, cooked in a wood-fired oven. It has become a global culinary icon, with countless regional and international variations, making it one of the most beloved and versatile foods globally.

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