The first was Star Trek VI: The Undiscovered Country. It was the last Star Trek movie with all of the TOS crew (some were in Star Trek: Generations). That Star Trek VI was a cold war ending allegory could hardly be more obvious. I've discussed a bit of this movie before. Not sure why I watched it. I guess I felt as if I hadn't seen it for a while.
The second movie I watched was the 1954 Disney version of 20,000 Leagues under the Sea. To be honest, I'm not sure what inspired me to watch it. It was based on the 1868 book by Jules Verne Twenty Thousand Leagues Under the Seas. The movie starred James Mason as Captain Nemo, Kirk Douglas as an American whaler, and Peter Lorre as the French professor's apprentice. Those were the only actors I recognized.
I know I'd seen 20,000 Leagues under the Sea before as a kid, maybe in the theater. In the 1960s and early '70s, Disney would re-release its live-action and animated movies because, for some reason, they weren't making new ones. In any case, I know I've seen that movie before. Also, I'm not sure but I might have read the book (translated to English, of course). I know I read Journey to the Center of the Earth by Verne when I was a kid. Later in life I read Around the World in Eighty Days.
20,000 Leagues under the Sea is about a submarine (very much science fiction in 1868) named Nautilus that attacks ships by ramming them. It is powered by a mysterious, abundant source of energy. This is why the first nuclear submarine in the U.S. Navy was named Nautilus after the submarine in the book/movie.
But how are they linked?
Warning: SPOILERS ahead.
In Star Trek VI, Kirk and McCoy are accused of killing the Klingon chancellor. At their trial they are sentenced to the prison asteroid of Rura Penthe, known throughout the galaxy as "the Aliens' Graveyard."
In 20,000 Leagues under the Sea, Captain Nemo takes the professor to see Rura Penthe, "the white mans' graveyard."
I bought the Kindle version of the Vern book for 29 cents (31 cents with tax). I searched for "Rura Penthe" and "graveyard" and neither came up. So I'm thinking it's only in the movie.
The writers of Star Trek VI snuck in a Jules Verne and/or Disney reference in the movie. The screenplay was written by Nicholas Meyer and Denny Martin Flinn. I would think it was Meyer (who also directed) who snuck in that reference. He likes to do that in his movies.
But if I hadn't watched the movies back-to-back, I would probably have never made that connection.