The indigenous Killiks built the Castle Lands of Oroboro circa 35,000 BBY. At some point, the Killiks colonized nearby Alsakan. They were taken away from Alderaan 30,000 BBY by the Celestials after consuming all of Alderaan's natural resources, and long believed extinct by humanity until re-encountered in the Unknown Regions. Human colonists came to the planet from Coruscant in 27,500 BBY and built a peaceful civilization in harmony with nature. Alderaan was a Core Founder of the Galactic Republic in 25,000 BBY and one of the anchor points for early hyperspace exploration. Alderaan was headquarters of Alderaan Royal Engineers, an early Republic shipwright. Alderaanian colonists settled Nim Drovis. In 27 BBY, it was personally protected by Jedi Master Eeth Koth during the Ashaar Khorda crisis.
Rebellious elements seek shelter on Alderaan
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Rebellious elements seek shelter on Alderaan

As a whole, Alderaan strongly opposed the Military Creation Act, but remained loyal to the Republic during the Clone Wars. Alderaan allowed Refugee Relief Movement settlement by displaced exiles from Ando and other Separatist worlds whom wished to remain Republic citizens. During the Clone Wars, Alderaan was attacked personally by General Grievous and took heavy damage, nearly "being destroyed." With the rise of the New Order, Queen Breha Organa and Senator Viceroy Bail Organa adopted Leia Amidala Skywalker. The Empire violently terminated the Jedi praxeum on the planet, though a few students escaped. Shortly afterwards, Jedi Knight Ylenic It'kla led a remnant of the Caamasi people to settle on Alderaan after Palpatine desolated Caamas. Ylenic served as Trustant of the Caamasi Remnant and advisor to the Organas.

After the horrors of the Clone Wars, Alderaan's frigates and light cruisers were dismantled and the world's weapons were placed aboard the armory warship Another Chance. The ship was programmed to continually jump though hyperspace until called home by the High Council. They would not have the opportunity. Immediately after the formation of the Empire, Alderaan was wracked by anti-Imperial protests, mainly from alien refugees who were now forced to pay an exorbitant tax to return home.
Alderaan destroyed
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Alderaan destroyed

When Bail Organa, Garm Bel Iblis, and Mon Mothma formally created the Rebel Alliance, many Alderaanians volunteered their resources and lives, despite the still fresh memories of the Clone Wars. Many of the early warriors of the Alliance, and subsequently, many of its leaders and officers, were Alderaanian.

Alderaan was the first strategic target of the first Death Star. In a demonstration of its power to Princess Leia, Grand Moff Tarkin ordered the destruction of her home. While she claimed the planet was weaponless, it is said it had some of the strongest defenses in the Empire. The plan backfired drastically, driving thousands of beings to the Alliance cause and sending many planets in the Mid Rim into open rebellion. The Imperials attempted to pin the blame for Alderaan's destruction on the Rebels, keeping a small number of people loyal to the Empire; however, it convinced few.

The remains of Alderaan became known as the Graveyard, and many Alderaanians who were offplanet when Alderaan was destroyed returned each year to leave memorials among the rubble for their lost loved ones.