The Shi'ar is a race of humanoids of avian descent; they resemble humans with feathered crests atop their heads in lieu of hair. They are one of the major alien empires alongside the Kree and the Skrull Empires.
The Shi'ar Empire consists of a vast collection of alien species, cultures and worlds. The Shi'ar Emperor of the time, Kral'Nor, was ambitious and expanded his empire. When the people of Krypton reactivated the World-Gate network, Kral'Nor wanted to use the network to conquer nearby star systems. The Kryptonians tried to reason with Kral'Nor until they had no choice but to call back every Kryptonian to Krypton, and shut down the network. As a result, the Shi'ar laid a five-year siege on Krypton despite the Kryptonians establishing a massive, impenetrable shield around their planet, initiating the Krypton-Shi'ar War.
In the sixth year of the siege, the Kryptonian Defense Force, led by General Zod, made a daring move in using a World-Gate to travel to the Battlestation Sentrius and used its powerful weapon system in instantly decimating the Shi'ar Imperial Navy. The heavy losses was a humiliating blow to the Shi'ar that became the catalyst for Emperor Kral'Nor to be overthrown and exiled by a group of Shi'ar that opposed the war, led by another of the Imperial Family. The New Shi'ar Empire quickly negotiated for peace and ending the war. The Shi'ar government would later reconstituted into the Shi'ar Republic led by Kral'Nor's daughter Lilandra Neramani. However, the aftermath of the Krypton-Shi'ar War had thrown the Shi'ar Republic to barely escape its economic depression in which it is furthermore exacerbated by a civil war between the the Republic and the loyal remnants of the Shi'ar Empire, which is led by Kral'Nor's children D'Ken and Cal'syee.