The Great War in Greek mythology refers to a global and catastrophic war between the Gods and the Titans, which would ultimately determine who would have control over the Earth. The Titans effectively lost the war after Zeus used the Blade of Olympus to end the war in one swift and decisive action.
However, Kratos returns to the time of The Great War in God of War II with the help of the Loom of Fate, aiming to change the course of history and prevent Zeus from unleashing the destructive power of the Blade Of Olympus. God of War II ends with Kratos and the Titans scaling Mount Olympus, and it is believed that God of War III will pick up directly from where it's predecessor left off.
The Great War is undoubtedly one of the most important events referred to, as of yet, in the God of War series. Its outcome is essential to the path that Kratos would tread in his later years, and as such, it has been an ever-present narrative device in every God of War game thus far.