Most monarchs tend to take power through hereditary means. Monarchs come to power by inheriting it. When the reigning monarch dies the oldest son, or daughters in some places, inherits the monarchy if they are willing to take it. Each kingdom operates differently, even today. England recently created a law that would allow the crown to pass to William and Kate's daughter, had she been the first born. Meanwhile in Japan, the princess had to abdicate due to her impending marriage to a commoner. Harry's impending marriage to an American divorcee has many talking about Wallis Simpson and her affair with Edward, Prince of Wales. The biggest difference between the two is that Megan Markle isn't currently married and Harry isn't the next in line to the throne.