In 1906, the San Francisco earthquake caused a huge fire that destroyed public birth documents. Suddenly a new opportunity for citizenship arose: Chinese men who were already in the United States could claim that they were born in the United States. Other Chinese men would travel back to China as United States citizens and report that their wives had given birth to a son. Consequently, this made the child eligible to be a United States citizen, for which they would receive a document. These documents could then be used for their actual sons, or sold to friends, neighbors, and strangers. This was termed as a "slot" and would then be available for purchase to men who had no blood relationships in the United States in order to be eligible to enter the United States. Merchant brokers often acted as middlemen to handle the sale of slots.