The defensive-only doctrine, alternatively referred to as the Ascendancy honor code, Chiss codes of conduct, or non-aggression laws, represented a foundational legal principle within the Chiss Ascendancy. This law strictly prohibited initiating hostilities in warfare, with violations resulting in the severe punishment of exile. The Aristocra, the ruling class, and the Chiss Academy heavily influenced Chiss society to view pre-emptive attacks as a grave transgression. This legal and social norm had been in effect for a millennium, specifically 1,000 years, prior to 22 ABY, and it served as a cornerstone of Chiss societal values.
Mitth'raw'nuruodo, the Chiss Force Commander, more widely known as Thrawn, committed a breach of this law in 27 BBY. He destroyed the Republic starship named Outbound Flight. Despite this violation, Thrawn successfully persuaded the Ruling Families to permit him to maintain his position, although this act created animosity towards him. After a subsequent violation of the same law during another conflict, Thrawn was ultimately stripped of his rank and banished to a remote planet located at the edge of Imperial space, where Voss Parck later rescued him.
In the year 22 ABY, the Nine Ruling Families engaged in intense discussions and debates surrounding the issue of preemptive strikes and their established defensive-only policy.
Luke Skywalker speculated in 36 ABY that the Chiss Ascendancy may have abandoned this long-standing law as a consequence of evolving galactic circumstances. He thought this may have been a factor in the Swarm War with the Killik Colony. Jacen Solo, being fully aware of the Chiss's stance against preemptive attacks, deliberately attempted to frame the Killiks for the attack on a Chiss supply depot situated at Thrago. His intention was to provoke the Chiss into launching a retaliatory strike.
The Chiss prohibition against initiating attacks was initially introduced in Vision of the Future, a novel penned by Timothy Zahn and released in 1998 through Bantam Spectra. Zahn's 2006 novel, Outbound Flight, formally identified this principle as the "defensive-only doctrine."
This particular law bears resemblance to a philosophical concept found in real-world political thought. It is similar to the non-aggression principle, which is a core axiom within individualist philosophy.