The "The United Monarchy " refers to the relatively brief period in the the history of ancient Israel and Judah when they were united under a single monarch. Primarily three kings. Saul's reign ends with a devastating defeat at the hands of the Philistines. David's, viewed by the author of Samuel-Kings as well as the Chronicler as the golden age, is marred by his affair with Bathsheba, his murder of her husband, and an internal rebellion. Solomon's is probably closer to what we would think of a golden age (characterized by wealth and international prestige), but his political marriages, according to the Biblical authors, end up leading astray from pure Yahweh worship.

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King David with harp, rebec, & psaltery.
Jean de Mandeville, Paris. J. Paul Getty Museum, Los Angeles, CA.