The Sylean-Chanestin war was a 109 year conflict between the Sylean Federation and the Chanestin Kingdom. The war started in -107 with the arrival of a Sylean trade mission at Keshi (Core 1938). The Chanestin, overly afraid of the ideas presented by the Syleans, had the entire mission executed. Later that year, with the trade mission overdue, the Syleans sent a military expedition to find out what happened. When the Syleans refused to quit Chanestin space quickly enough, the Chanestin local defense forces opened fire.
Chanestin initially had the upper hand, and by -102 had conquered several Sylean worlds. Chanestin policy regarding conquered worlds required significant time to implement and they paused. This forced a stand-off which lasted for some thirty years while agents on both sides attempted to incite rebellion on each other's worlds.
In -69, the Syleans launched an offensive to recapture their lost worlds. This offensive started well, but soon developed into a war of attrition, and minor skirmishes continued for the next twenty-five years, with many worlds changing hands several times. By -44, both sides were worn out and a peace treaty was finally agreed to. Despite this, the two periods of conflict are regarded as phases of a single war, and the period between -44 and -25 as just a hiatus.
When the Sylean Federation began its expansionist policy under Cleon, Chanestin saw this for the threat it undoubtedly was. In -25 they launched a daring deep strike against the Sylean industrial world of Shudusham. War flared again, but now Sylea had the techological edge. The Chanestin did not admit defeat easily, and their strategy of launching deep strikes into the Sylean heartland placed the whole of the Sylean Federation on a war footing.
From -3 onwards, Cleon carried the war deep into the Chanestin territory, and in 2 the flag of the new Imperium was finally raised above the Chanestin palace on Keshi. The Chanestins finally knew they were beaten, and sued for peace.