why is new england reffered to as daughter and a limb of old england?

Bradstreet styled this poem as a dialogue between Old England, the mother, and her daughter, New England. New England asks her mother why she is suffering and mournful, especially since she possesses more wealth and national glory. The mother wonders if her daughter is ignorant of her woes, and warns her child that if she dies, her daughter will die along with her (indicating that New England was of course founded by and is administered by Old England). New England then tries to speculate the cause of her mother’s grief. She lists all the possible reasons for her mother's turmoil, citing events from England’s past, like the Anglo-Saxon conflicts, the Norman invasion, feudal rebellion, and the War of the Roses, as well as asking if it is a natural problem such as drought, famine, or pestilence.