The Earth-Romulan War

In 2155 the Romulan Star Empire tried to wreck the rapprochement between Earth, Vulcan, Andoria and Tellar by sending remotely piloted ships able to disguise themselves as other vessels. Enterprise and its allies thwarted the plan, but the growing alliance was a direct threat to Romulan ambitions, and open war broke out the following year.

The conflict lasted from 2156 to 2160 and was fought with weapons that later generations would consider primitive, including atomic arms. It has never been shown in detail on screen, but its outlines are known: no human ever saw a Romulan face to face, and visual communication was never established throughout the fighting.

The war ended with a treaty negotiated entirely by subspace radio, which created a Neutral Zone between the two powers; entering it would be treated as an act of war. Its outcome strengthened the bonds that led to the Federation in 2161. The Romulans then withdrew into isolation for about a century, until 2266, when the crew of Kirk's Enterprise finally saw their faces.