The Sacking of Coruscant was the final major military maneuver of the Great Galactic War. Whilst the Sith Empire and the Galactic Republic took part in peace talks on Alderaan the Sith deviously pulled off their one final attack, an attempt to hit the Republic into a corner so that it agrees to the Empire's terms; because of the attack the Republic delegation had no other choice but agree to sign the Treaty of Coruscant which lost them many long-time allies by releasing control to the Empire. The Attack also paved the way for the long standing Cold War between the Republic and the Empire.
The battle began when a Sith shuttle carrying a large number of Sith warriors, lead by Darth Malgus, crashed in the Jedi Temple. The Jedi were taken by surprise. After a long fight, most of the Jedi and Jedi Temple Security forces were killed. After that battle, starfighters bombarded the surface of Coruscant.
After two days of Sith occupation Coruscant was returned to Galactic Republic following the signing of the Treaty of Coruscant. The Sith-biased treaty put the Republic into a state of weakness throughout the galaxy, this caused the reconstruction of Coruscant to be delayed and the lower levels to fall into the control of gangs. The Sith attack on Coruscant is still fresh in the minds of people and its effects could still be seen as late as the Second Great Galactic War.
The Sacking of Coruscant is featured in the Deceived trailer. Jedi Master Ven Zallow is shown dueling and ultimately falling to Darth Malgus in a fierce unequal combat.
- For information on this subject beyond The Old Republic, see: Sacking of Coruscant on Wookieepedia