Why was it so important for Henry viii to have a son?

Henry needed and heir to the throne of England, because traditionally, if he died without a living son, the kingdom would erupt into a civil war. Pretenders to the throne would be fighting to take power. Meanwhile, Nations neighboring England would seize the opportunity to invade while there was no one in power to lead a defense. The very future of England's existence hung on the King making the Queen pregnant with a healthy surviving son. What a burden huh?