South Sudan gained independence in 2011 and is the youngest country
Throughout history, there have been several waves of countries being conquered and then gaining independence. Most South American countries gained theirs during the first half of the 19th century, while many African and Asian countries underwent the same process after WWII.
The latest country to gain independence was South Sudan in 2011, after passing a referendum with 98.83 percent of the votes. They had spent 13 years fighting a civil war against what is now North Sudan.