WhenTheGunsFallSilent/Events
This details events in the backstory. This focuses largely on events different from canon Trek.
Cardassian Liberation War
A war that started in 2347, between the United Federation of Planets and Cardassia, with the Setlik III Massacre the final trigger on rising tensions between the two regional powers. When the Federation imposed strict sanctions on the Cardassian Union in 2320, following the occupation of Bajor, rising tensions and the increasing brutal rule of Bajor and other neutral planets caused tension. Finally, in 2347, with Cardassian attacks on Federation colonies ramping up, particularly after the Setlik III Massacre, the Federation declared war.
The war was hard at first for the Federation, and it led to a major reorganization of Starfleet and a shift in the outlook to a more militarized and defense focused posture that would persist for decades after the war. It was only after the Liberation of Bajor, in 2350, with the establishment of a forward base there on one of Bajor's moons, and the return of commodores as not just a courtesy rank, but as section commanders, that the tides shifted, to put Cardassian firmly on the back foot. The joining of the Romulan Star Empire, and joining of the Klingon Empire as a full member of the new Narenda Stellar Alliance.
This Alliance penetrated Cardassian space in mid 2352, and would have likely chased the Union back to the core systems if not for the surrender.
To ensure a neutral arbitrator in a war that had drawn easily eight-tenths of the known galaxy at the time, the Federation asked the Organians if they would be willing to mediate a treaty. The resulting 2352 Treaty of Organia, and reform of the Cardassian Union's ruling Central Command into the Detapa Council, ended the war and ended the Narenda Stellar Alliance, although the 2353 Khitomer Accords established many new interstellar organizations as a result of the war, including several Intellstellar Standards Bureaus.