A "metonym" is a word associated with a particular institution that is used in place of it. For example, "The Pentagon" in place of the United States Department of Defense, "Brussels" in place of the European Union, or "Hollywood" in place of the American film industry, and "The City" in place of the British financial sector.
This thread is for metonyms that you think might have come about in alternate history scenarios.
I'll start. If a Confederate States victory scenario, "Mechanic's Hall" would be a metonym for the Confederate War Department, as it had established itself in a Richmond building of that name and would likely remain there after the war was over.