  We prove that three strategy video games from the Sid Meier's Civilization
series: Sid Meier's Civilization: Beyond Earth, Sid Meier's Civilization V, and
Sid Meier's Civilization VI, are Turing complete. We achieve this by building
three universal Turing machines-one for each game-using only the elements
present in the games, and using their internal rules and mechanics as the
transition function. The existence of such machines imply that under the
assumptions made, the games are undecidable. We show constructions of these
machines within a running game session, and we provide a sample execution of an
algorithm-the three-state Busy Beaver-with one of our machines.
