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* Kzinti: Large and very aggressive felinoid aliens with whom humans fight several brutal interstellar wars.

Kzinti tactics are somewhat cat-like in nature, " scream and leap " being the primary mode of declaring a challenge.

The first Man-Kzin War ended when the humans obtained the faster-than-light drive ( FTL ) from the Outsiders, after which the Kzinti ships stood no chance against the FTL warships.

Throughout the rest of the wars with man, the Kzinti tended to always attack before they were ready, and subsequently lost all of them.

As a result of this most of their empire was lost ; in the peace treaties that resulted, colonies and slave planets were ceded to man or given independence.

In Ringworld it is revealed that this was in part due to clandestine meddling by the Pierson's Puppeteers.

They saw in the aggressive Kzinti a major threat, and orchestrated the events that led to the humans getting FTL ships and thereby ensuring the human victory of the first war.

Each of these Kzinti defeats eliminated the most aggressive individuals from the Kzinti gene pool and thus made the Kzinti more " manageable " from a Puppeteer point of view.

By the time Ringworld takes place, Kzinti are able to deal with other races diplomatically, rather than by attacking and enslaving them.

Female Kzinti are not sapient, although among the archaic Kzinti found on the Ringworld some are.

The protagonist Louis Wu thinks this indicates the Kzinti in Known Space have bred intelligence out of their females.