Can the King be Captured?

Why isn't the King captured in the game of Chess?

During olden days, when there was the concept of Kingdom and coronation of the male child of the King, wars were common and each King would plot on how to attack another kingdom to add to his valour.

Chess has a similar concept, about "checkmating" the opponent. You can capture pawns, rooks, knights, bishops and the Queen, but have you ever wondered why the King isn't captured? There are various things that various people say about the issue.

It is believed that during a War, if the King is captured and killed, his male child (if he has an heir), will be crowned the King when he comes of age and the conquered kingdom will have to be rightfully returned to him, or an other war ensues.

On the other hand, if the King is conquered and kept alive (something like checkmate), the heir cannot be crowned, because the King is still alive. So it is as good as the Kingdom belonging to the opponent.

Probably keeping this in mind, Chess rules has it that the King cannot be captured. Chess revolves around the immense piece called the King. If you have come across any other ideas on this issue, please feel free to discuss.