1) The ongoing conflict in Syria, which began in 2011, has resulted in a humanitarian crisis, displacement of millions of people, and international efforts to bring about a resolution and provide aid to those affected.

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) The highest-grossing concert tour of all time is U2's "360° Tour," which earned over $735 million in ticket sales.

4) The concept of sovereignty refers to the supreme authority and power of a state to govern itself, make decisions, and control its own territory without interference from external forces.