Captain America: Civil War - 30 Easter Eggs & References You Must See

3. The Manchurian Candidate

In the final sequence when Iron Man goes to Siberia to offer Cap and Bucky his support (before Zemo reveals The Winter Soldier killed his parents), Tony Stark calls Bucky "Manchurian Candidate".

That's obviously in reference to the 1962 movie (and in turn Richard Condon's 1957 novel) - which was also adapted in 2004, to less success - which focuses on American soldiers being captured by the Soviets and brainwashed and turned into assassins. Instead of trigger words, the assassins are activated in that film using playing cards, but it's a very similar narrative.