See Balance of terror for the Cold War policy.
"Balance of Terror" was an early episode of the original series of Star Trek. It was first shown on December 15, 1966, and introduced the first recurring foe: the Romulans. The captain of the Romulan ship was played by Mark Lenard, who would later play Sarek. It has been described as a '1950s submarine movie in space', and was written by Paul Schneider.

The Starship Enterprise is sent to persue a ship that has destroyed Earth Outpost 4; near the Romulan Neutral Zone. It is feared that after a century of non-contact, the Romulans have built up their forces again. Kirk gets there and discovers a lone ship, that has an ability which surprises the entire crew, Mr. Spock included - it has a cloaking device.

The Enterprise finds that this is not perfect and manages to track the ship - it is returning home after what appears to have been a test of strength. The Enterprise taps into the Romulans internal security cameras and makes another astonishing discovery : the Romulans are, in appearance, identical to the Vulcans, a member world of the United Federation of Planets. Mr. Spock denies all knowledge of this.

The episode ends with the Enterprise finally cornering the Romulan Bird of Prey; after a battle, the Enterprise is victorious and offers to take on survivors: but the Romulans self-destruct, rather dying than being taken prisoner.