1) The concept of separation of powers, as articulated by French philosopher Montesquieu, refers to the division of government responsibilities into distinct branches, such as the executive, legislative, and judicial, to prevent concentration of power.

2) Michael Phelps, an American swimmer, has won a total of 28 Olympic medals, including 23 gold medals, making him the most decorated Olympian of all time.

3) The Mongol Empire, under the leadership of Genghis Khan, became the largest contiguous empire in history, spanning from Asia to Europe.

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