Q: This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.
The region, as part of Lorraine, was part of the Holy Roman Empire, and then was gradually annexed by France in the 17th century, and formalized as one of the provinces of France. The Calvinist manufacturing republic of Mulhouse, known as Stadtrepublik Mülhausen, became a part of Alsace after a vote by its citizens on 4 January 1798. Alsace is frequently mentioned with and as part of Lorraine and the former duchy of Lorraine, since it was a vital part of the duchy, and later because German possession as the imperial province (Alsace-Lorraine, 1871–1918) was contested in the 19th and 20th centuries; France and Germany exchanged control of parts of Lorraine (including Alsace) four times in 75 years.
A:
When did Stadtrepublik become a part of Alsace?