Easier way: From legends mode, 'p' for 'export map/gen info'. Then have a look in your dwarffortress directory. There will be a file called 'someworld-00125-01-01-world_sites_and_pops.txt' (where the numbers are the game date that you exported the info. Look for the cities in that file and take a look at the "Paren Civ" line. If it is missing, it's because the city is ruined. You can also look at the 'blah-blah-world_history.txt' file to see who the current king is, etc.
Now, once you've verified the ownership of the cities, you can go into legends mode and look at what's happened to the city. You can either look at "sites" or somethings it is easier (if you suspect that a war happened), to go and look in "The Age of <whatever>" and look for conflicts with those civs. As long as the sites involved existed at least 10 years previously you can also search for the sites on the "Historical Maps". Using that you can see what influence each civ has around the site. It helps if you already know where to look -- using a tool like legends viewer or legends browser can often help a lot.
My guess is that your civ defeated the elves in that site and took over the forest retreat. If they, in turn, lost every other site, I suppose it could become the mountain home. If so, it would be interesting to visit it in adventure mode to see what it looked like.