El señor feudal ofrecía protección a sus vasallos, pero ellos entonces quedaban a su merced.A feudal lord would offer protection to his vassals, but they were then at his mercy.
Es una niña malcriada que hace lo que le da la gana, y los padres están a su merced.She's a spoiled child who does whatever she wants, and her parents are at her mercy.
Solo usted puede salvarnos de la quiebra prestándonos ese dinero. Estamos a su merced.Only you can save us from bankruptcy by lending us that money. We're at your mercy.