Why do some old books and films have two titles?

Like: Futility, or The Wreck of the Titan(that's all one title), or of course Dr. Strangeglove or: How I learned to stop worrying and love the bomb.
 
 There are various other examples I can't recall right now. This is driving me nuts, and I can't find anything on Google except someone asking the same question (no answers). Is there a proper name for this practice?
 
BTW just curious.
 

 

" Frankenstein; or, The Modern Prometheus is another example of this. I think it's probably just an older way of doing subtitles that fell out of fashion.
 
Uncharted 3; or, Drake's Deception does have a nice ring to it though. "

Different names in different places... Wasn't Northern Lights known as the Golden Compass in America? The only example I can think of right now, but there have been a lot more.

" Uncharted 3; or, Drake's Deception does have a nice ring to it though. "

The Wreck of the Titan was changed to Futility in the 1912 re-print. I think it probably had to do with the similarities between the Titan and the Titanic. Titan was written before the Titanic sank.
As for a lot of other things; it usually has to do with localization.