It certainly was not the first peaceful turn-over of power in history - there are many examples, but Cincinnatus[1] immediately sprang to my mind. He actually was given and then gave up dictatorial powers twice (note that being a dictator meant in the Roman political system something different than what it means today [2]).
Just a small clarification: in OE ð and þ were used interchangeably. Between voiced sounds they were pronounced as in Modern English "then", otherwise as in Modern English "thin".
[1] https://en.wikipedia.org/wiki/Lucius_Quinctius_Cincinnatus
[2] https://en.wikipedia.org/wiki/Roman_dictator