There are two post-credit conversations in the game. The first is between Snake and Miller, where Snake explains that he feels that The Boss betrayed him because she put down her gun and rejected everything in her life up to that point, including him. Snake then proclaims that he'll never do that and finally accepts the title of Big Boss. The second post-credit scene is Snake giving a speech to all of his men at Mother Base, declaring them as Outer Heaven.
After the ending of the main game, there is a time line that shows events that happened over the next 31 years, including Huey becoming a father and naming his son Hal in 1980, Big Boss triggering the Outer Heaven uprising in 1995, and Miller being found assassinated in his home by an unknown assailant in 2005.
The game begins with the quote "Peace Amongst men living alongside one another is not a natural state. On the contrary, the natural state of man is that of war. War manifested not only by open hostilities, but also by the constant threat of hostility. Peace, therefore, is a state that must be established by law." - Immanuel Kant, "Perpetual Peace" Chapter 2