Sydney was Australia's largest city and most important port, and the capital of the state of New South Wales. Even by 2047, the city remained a pristine Blue Zone and largely unaffected by the global Tiberium infestation. A massive wall surrounded the city and protected it from the harsh Yellow Zone outside.
Sydney was also the GDI HQ for the Australia-New Zealand Theatre of War, serving to counter the Nod HQ at Ayers Rock. A clash between the major GDI and Nod forces in the region would seem inevitable.
The first encounter in the A-NZ theatre was when a group of elite Nod troops intercepted and secured a hazardous materials transport of GDI, which carried nuclear warheads. However, before they could manage to relocate them, the Scrin attacked.
Kilian Qatar, acting commander-in-chief of Nod decided to join forces with the GDI in the area to turn back the invaders at Sydney. However, she also had an ulterior motive; to steal the nuclear launch codes for the stolen warheads from GDI's command center in Sydney.
The Scrin attacked Sydney, and GDI attempted to hold the line. Eventually the city walls were breached, and Nod managed to sneak a saboteur inside the command center and steal the codes. Nod also took the opportunity to disable the ion cannon control bunker in the vincinity.
Later, despite a moderately successful holding action at the city walls, the Scrin managed to establish a foothold in Downtown Sydney, by the docks. Nod covered GDI's forces as they were being airlifted to safety. However, to the astonishment of the Nod forces, Kane contacted them, revealing himself to be alive. He immediately ordered the destruction of GDI forces in Sydney, authorizing the commander to use the stolen nuclear missiles.