Answer the following question: Given the following passage  "During the regency of Maria Cristina, Espartero ruled Spain for two years as its 18th Prime Minister from 16 September 1840 to 21 May 1841. Under his progressive government the old regime was tenuously reconciled to his liberal policies. During this period of upheaval in the provinces he declared that all the estates of the Church, its congregations, and its religious orders were national property—though in Valencia, most of this property was subsequently acquired by the local bourgeoisie. City life in Valencia carried on in a revolutionary climate, with frequent clashes between liberals and republicans, and the constant threat of reprisals by the Carlist troops of General Cabrera.",  answer the following question. Note that the answer is present within the text.  Question: In what month did Espartero's rule end?
Answer:
May