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:
Guinea-Bissau

Context:
Guinea-Bissau is a republic. In the past, the government had been highly centralized. Multi-party governance was not established until mid-1991. The president is the head of state and the prime minister is the head of government. Since 1974, no president has successfully served a full five-year term.

Question:
When was multi-party governance established?

mid-1991