Thanagar began in ancient times as a hard world with a primitive and savage culture. Its inhabitants possessed extensive knowledge of agriculture, mathematics, and philosophy, achieving many developments in technological advancement. Among these was the utilization of Nth metal, a strong metal known for it's ability to negate gravity, making it perfect for the flying Thanagarians.
The Thanagarians once worshiped a pantheon of extradimensional entities known as The Great Old Ones. As they matured the Thanagarians stopped worshiping them and 21st Century Thanagarians bowed down to no higher power. As Hawkgirl proclaimed, her race was a warlike people, and sometime after the utilization of Nth metal, the Thanagarians began a conquest of neighboring planets and star systems. They established an intergalactic sense of hegemony known as the Thanagarian Empire.
The Thanagarian-Gordanian War
With the expansion of its military forces throughout its many years of conquest, the inhabitants of Thanagar eventually came into contact with the Gordanians, a cruel race of intergalactic slavers. Skirmishes over territory between the two worlds eventually escalated into an all-out war, known as the Thanagarian-Gordanian War. A long and bloody war, the period of conflict saw heavy casualties on both sides. In the later years of the conflict, however, the situation grew considerably worse for Thanagar, with the Gordanians closing in on the planet, as it appeared the Gordanians would emerge victorious. The Thanagarians then sent an agent, Lieutenant Shayera Hol, to Earth in order to ensure an "alliance" between the two planets.
Invasion and Occupation
The alliance was established with Earth, and, shortly after the "Gordanians" began an apparent attempt to invade Earth. The Thanagarians then arrived, offering to construct a planetary force field to aid Earth's inhabitants in fending off the impending threat; however, the Gordanian invasion of Earth was revealed a false flag operation engineered by the Thanagarians and the planetary force field was in reality a Hyperspace Bypass Generator, which the Thanagarians would use to lead a direct assault on the Gordanian homeworld and end the war, though at the cost of Earth's destruction; a fact that Thanagarian general Hro Talak stated was a necessary sacrifice for the sake of Thanagar. The Thanagarians then began their invasion of Earth, taking control of the Justice League's Watchtower, and as Earth's protectors were forced into hiding, began construction on the bypass generator. The subsequent occupation of Earth was one of exceptional brutality, as those who attempted to fight back faced imprisonment and torture. Because of this, Shayera Hol betrayed her people, with the Justice League launching its counterattack, resulting in the destruction of the Thanagarian fleet sent to support the occupation. The final blow, however, was delivered in the form of Batman manually guiding the Watchtower to crash into the generator, as with its destruction, the Thanagarians were forced to leave Earth.
Following the destruction of the hyper-space bypass generator, along with a significant portion of its fleet, Thanagar was assaulted by the full force of the Gordanian fleet. In a desperate move, General Hro Talak led a suicide attack, ramming his command ship into the Gordanian flagship, the subsequent explosion resulting in the destruction of a majority of the Gordanian fleet. However, the general's sacrifice proved to be in vain, as the remaining forces of the Gordanian fleet then closed in on Thanagar, securing its victory.