Continuity — There is some confusion over the number of Man-Kzin Wars, as well as the distinction between what is officially recognized as a "war" and what is a major Kzinti "incident".
(a) Nessus, talking to Speaker-To-Animals (a Kzin), says "Six times over several centuries, you attacked the worlds of men. Six times you were defeated, having lost approximately two-thirds of your male population in each war" (Ringworld ch. 2, p. 19). The most obvious interpretation of this statement is there were six Man-Kzin Wars.
(b) Yet elsewhere in the same account, Speaker-To-Animals refers to only four wars: "You kept winning, Louis. For three centuries and four wars you had been winning" (Ringworld ch. 16, p. 237).
(c) In a much more recent publication, Niven seems to clear up the contradiction:
There were major "incidents" as well as the four wars. ("The Soft Weapon" in Neutron Star describes a minor "incident.") "Six times over several centuries, the kzinti attacked the worlds of men..." I've forgotten where the quote comes from, but at least two "incidents" must have been major ones.
—"Canon for the Man-Kzin Wars" (Scatterbrain p. 293)
(d) "Fly-By-Night" specifies the Fourth Man-Kzin War ended in 2505, when the Covenants of Sasht were negotiated (Man-Kzin Wars IX pp. 308-9). The Covenants are still in effect during the time of that account, in 2656. Therefore, at least officially, 2505 was the end of the Man-Kzin Wars.
(e) As noted, Beowulf Shaeffer mentions a "war" circa 2615, well after the "official" end of the wars ("Flatlander", Neutron Star p. 129). We presume this was one of the two "unofficial" wars, although it's possible not everyone who counts six wars counts the same two "major incidents" as wars.
(f) In 2650, Achilles (a Puppeteer) thinks "How odd it was that the timidity of Kzinti had brought him to this [...] Six disastrous wars had rendered the ‘Heroes’ impotent as a counterweight to the humans" (Juggler of Worlds ch. 26, p. 131). This appears consistent with Nessus’ statement in Ringworld; apparently the Puppeteers count six Man-Kzin Wars.
(g) "For two hundred and fifty years the kzinti had not attacked human space" (Ringworld ch. 2, p. 18), indicating peace since circa 2650. This is supported by Achilles’ internal monologue, as noted in (f) above. But as noted in the main entry, the idea of a permanent peace treaty is foreign to the Kzinti culture. Speaker-To-Animals said "In the dark days that followed the Fourth Truce with Man..." (Ringworld ch. 17, p. 237). Also: "To the Patriarchy, the last disastrous interstellar war is still officially the ‘Fourth Truce with Man’..." (Ringworld Role-Playing Game— Explorer Book p. 50).
(h) We also suggest the major difference between an "official" war and an "unofficial" one is that at the end of each official war, an official armistice was signed with the Patriarchy. It may be that in the "unofficial" wars, the war ended in a cease-fire, with no official armistice or peace treaty being signed afterward (as with the Korean War, which ended in 1953 with no official peace treaty following). Or, it may be that the "unofficial" wars were started without any official sanction by the Patriarchy, and the Kzinti participating were eventually declared by the Patriarchy to be "rebels". Given the Patriarchy's clandestine sanction of Kzinti "incidents", as noted in "The Soft Weapon" and "Fly-By-Night", it seems entirely possible that the Patriarchy would wait to see how well a new war was progressing before deciding to either sanction it or declare it a "rebellion".
(j) Regarding the date of the end of the First Man-Kzin War: Ringworld Roleplaying Game— Explorer Book states "The hyperdrive armadas of 2410-2420 finally drive the Kzinti invaders from Human Space, ending the war in a grinding defeat for Kzin's ruling Patriarchy" (p. 30). The beginning date of 2410 is not compatible with various other canonical sources. Humans first obtained the hyperdrive from Outsiders in 2409 (Destroyer of Worlds ch. 51, p. 285). The first hyperdrive ship arrived at Sol System two years later, with the crew unaware of the war (interstitial notes in Tales of Known Space p. 151). Therefore, there could not possibly have been any Human hyperdrive armadas prior to 2411, and realistically probably not until 2412 or later. But the Game’s date of 2420 as the end of the war does not contradict any canonical reference.
Science — Man-Kzin Wars author Paul Chafe argues that the Man-Kzin Wars could not have produced a significantly less aggressive Kzinti species, because despite the wars it is still the most aggressive males who win property and breeding rights, when competing with each other. He also argues that the culling of only four or six generations is not enough to produce a significant genetic change. We agree that it is reasonable to suggest the change may have more cultural than genetic. However, we note that on Earth, lions have evolved to avoid attacking Humans, despite the fact that they still compete among themselves for breeding rights in much the way Kzinti do. By extension, it seems clear that after the Wars the Kzinti were still as aggressive toward each other, but not as aggressive toward Humans; and perhaps not towards other species, as well. We also note that modern evolutionary research has shown that changes can happen with surprising swiftness. Therefore, we consider it entirely possible for the wars to have caused a real genetic change, although perhaps one less radical than Ringworld indicates.↵