Earth-Romulan War

The Earth-Romulan War was a major interstellar conflict fought during the mid-22nd century between the forces of United Earth and those of the Romulan Star Empire, and their respective allies.

History
Sometime just prior to November 2157 the Battle of Galorndon Core was fought between the two powers and won by United Earth, though it was a costly and bloody event, described by Captain Wilson as "a nightmare".

During November of that year the Pioneer was sent to the planet Vorkado to investigate a reported collaboration between the Romulans and the Tholians (indeed both sides would have benefitted from such an alliance), however this sparked the Battle of Vorkado. By this time the Andorians and Kzinti, who's territory was under threat, were also assisting Earth and the "Daedalus project" had been accelerated to assist in the war effort. (: "Yesterday's Pioneer")

The Battle of Sector 2148 was a decisive strike by United Earth and MACO forces which stopped the Romulans from staging an invasion of Earth. (Star Trek: Poseidon - The Birth of the Coalition)

The war was ended with the Battle of Cheron. A stunning victory for Earth it ended the Romulan threat to the planet and the Romulans negotiated a treaty that would create a neutral zone to act as a buffer between the Romulan Star Empire and Earth territory.