Defensive-only doctrine
The defensive-only doctrine—also referred to as the Ascendancy honor code, the Chiss codes of conduct, or non-aggression laws—constituted a key legal framework within the Chiss Ascendancy. This framework explicitly prohibited initiating acts of war, with violators facing punishment through exile. The Aristocra, who held significant power, along with the Chiss Academy, heavily influenced Chiss society to view pre-emptive attacks as unacceptable. This legal principle had been a cornerstone of Chiss society for a millennium (1,000 years) before 22 ABY.
Mitth'raw'nuruodo, the Chiss Force Commander better known as Thrawn, acted against this law in 27 BBY when he destroyed the Republic starship Outbound Flight. Despite this violation, Thrawn managed to persuade the Ruling Families to allow him to remain in his position, though not without creating animosity. After a second breach of the law during another conflict, Thrawn was stripped of his rank and banished to a planet situated at the edge of Imperial territory, where Voss Parck later found him.
In 22 ABY, the Nine Ruling Families engaged in intense debate regarding the defensive-only doctrine and the issue of preemptive strikes.
Luke Skywalker speculated in 36 ABY that the Chiss Ascendancy might have abandoned this law due to evolving circumstances in the galaxy. He considered this as a potential factor in the Swarm War with the Killik Colony. Jacen Solo, fully aware of the Chiss stance against preemptive attacks, made an attempt to falsely attribute the attack on a Chiss supply depot at Thrago to the Killiks, with the intention of provoking a retaliatory strike from the Chiss.
Behind the scenes
The Chiss principle that outlawed first strikes was initially introduced in Vision of the Future, a novel authored by Timothy Zahn and released in 1998 through Bantam Spectra. Zahn's 2006 novel, Outbound Flight, later identified this principle as the "defensive-only doctrine."
This legal principle bears resemblance to a real-world political concept known as the non-aggression principle, which serves as a foundational tenet within individualist philosophy.