"Mozart in Mirrorshades" is a short science fiction story by Bruce Sterling and Lewis Shiner first published September 1985 in Omni.
The story's protagonist is a man named Rice, who works for a company that obtains natural resources and valuable artifacts from alternate timelines created in the past (whenever one engages in time travel, a new timeline forms, making it impossible to alter the original history).
The American Revolution has occurred, but it was carried out with the support of the company, which used it as an opportunity to establish a puppet government in North America.
Due to the activities of the company (possibly global warming caused by their drilling for and use of fossil fuels), large portions of Florida have become submerged by the ocean.
Although individuals from alternate timelines are not generally allowed to immigrate to Realtime (this requires a "Green Card", which is granted very rarely), the inhabitants want anything that they can get that is modern.
"Quiche-to-go" stores have been opened in France, and Napoleon Bonaparte is mentioned "chewing Dubble Bubble in Corsica".
After Rice is held captive for several hours in an isolated house, Jebe Noyon, a former Mongol warrior and member of the Grey Card Army (a Grey Card allows one to move between different branches of alternate history, but not enter Realtime), arrives.
At this point, Marie Antoinette arrives, shouting angrily at Mozart, who had promised that if she led Rice into the trap, he would obtain a Green Card for her.
Parker, the propaganda officer, casually kills Jebe, explaining that he could not risk anything happening to Mozart, whose music has reached number five on the Billboard charts.