TOS Season 1 Episode 23 A Taste of Armageddon

Plot

The USS Enterprise travels to Eminiar VII in NGC 321, bringing Ambassador Robert Fox to establish diplomatic relations. Little is known about Eminiar VII, beyond the fact that they have been at war with a neighboring planet, Vendikar.
Nearing Eminiar VII, the Enterprise receives a message from the planet warning them not to approach, but Ambassador Fox orders Captain Kirk to proceed. Kirk, First Officer Spock, and additional security personnel beam down to the planet, where they are met by representatives Mea 3 and Anan 7. During a supposed attack by Vendikar, Anan 7 explains that the war is conducted as a computer simulation, and that the Enterprise has been "destroyed" in the attack. The two planets have a treaty, according to which they have to kill the "victims" of every simulated attack. The crew are thereby expected to report to Eminiar's disintegration chambers for execution, and Kirk's party is taken captive. Spock telepathically plants a suggestion in their jailer's mind, allowing them to escape.
Anan 7 uses a voice duplicator to imitate Kirk's voice and order the crew to transport down. Scotty, suspicious, has the ship's computer analyze the message and confirms it is fake. He orders shields raised. When the crew fails to transport down, Eminiar fires upon them, but the attack is deflected by the shields. Anan 7 then contacts the Enterprise, claiming the attack was due to a malfunction. Ambassador Fox, deciding to believe Anan, beams down and is taken to a disintegration chamber along with Mea 3, who was also "killed" in the war simulation. Spock and the security officers rescue them.
Kirk confronts Anan 7 but is overpowered by guards and taken to the Eminian council chamber. When Anan 7 opens a channel to the Enterprise, Kirk orders Scotty to execute General Order 24 before being cut off. Kirk explains that he just ordered the ship to destroy everything on the planet within two hours. Panic ensues, which Kirk takes advantage of to disarm the guards. After Spock arrives, Kirk destroys the war simulation computers. Anan 7 condemns Kirk's actions, arguing that it is unalterable nature to fight wars, so without the simulation they have no alternative but to fight a real war. Kirk instead believes that the only reason the war with Vendikar has gone on so long is because the simulation insulated both societies from the horrors of war and gave them little reason to end it. He convinces Anan 7 to call a ceasefire and begin peace negotiations, and Fox agrees to act as a neutral mediator between the planets.