The First Man-Kzin War was the first conflict between Kzinti and Humans.
It started when a Kzinti warship attacked the Earth colony Wunderland in the Alpha Centauri system in 2367. Humans were totally unprepared militarily since inter-Human conflicts had ceased and no planetary defense was necessary. One of their primary weapons of the Human forces against the Kzinti was the exhaust of their reaction drive ships.[1]
When Outsider ships visited the Procyon system, Humans of We Made It colony bought the Hyperdrive technology from them. The tide of the war turned and the war ended in 2420.[1]