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:
Chihuahua_(state)

Context:
A handful of families owned large estates (known as haciendas) and controlled the greater part of the land across the state while the vast majority of Chihuahuans were landless. The state economy was largely defined by ranching and mining. At the expense of the working class, the Díaz administration promoted economic growth by encouraging investment from foreign companies from the United Kingdom, France, Imperial Germany and the United States. The proletariat was often exploited, and found no legal protection or political recourse to redress injustices.

Question:
Diaz promoted economic growth by encouraging investment from foreign companies at the expense of what group?

working class