Kzinti Wars
The Kzinti Wars were a series of wars fought between Humans and the Kzinti sometime during the mid-to-late 21st century, which according to Hikaru Sulu, the last war between Kzinti and Humans "was two hundred years ago" from the standpoint of 2269. 

Though some Kzinti tasted the meat of Humans in the course of these conflicts, they ultimately lost all of these wars with Humankind.

Two centuries later, Sulu considered the Kzinti to have learned little since these wars, as they remained aggressive despite being forbidden all weapons beyond police vessels by the Treaty of Sirius. 

Following the Kzini theft of a Slaver stasis box in 2269, and the subsequent neutralization of the Slaver weapon contained within, Spock found it "Strange, how the past sometimes breaks through into the present," and "that ancient war could have sparked a new war between man and Kzinti." ()

Appendices

Background information 
According to "The Soft Weapon", a short story written by Larry Niven from which the episode was originally adapted, this conflict was officially known as "Kzinti wars", and his expanded universe further described the events as the "". The first of the conflicts was fought with sublight vessels, with the Kzinti only being defeated thanks to Earth acquiring faster-than-light travel. Given the events presented in , which established that Earth's first recognized encounter with extraterrestrials occurred immediately after Zephram Cochrane's first manned warp flight in 2063, it is unlikely the nature of this conflict happened in the nature Niven's version indicated.

Furthermore, dialog from the  episode , which established that Humans still "had no idea" of what threats lay in space when the titular probe was launched in 2067, suggested that as of that point in time, the Kzinti were not yet known to Humans that point.

External link
 

de:Irdisch-Kzintianische Kriege
fr:Guerres Terre-Kzin
nl:Aarde-Kzin oorlogen
Earth conflicts