You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Valencia

Context:
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.

Question:
When did Espartero rule?

16 September 1840 to 21 May 1841