Ok. I am going to make a template for you to get some ideas from for the beginning story that leads into the war. things in parentheses are things you need to name.
In a far universe, there was a planet. It was called (Planet). There was a family on that planet that would contain the people who helped with important things on the planet. There were two brothers, (enemy) and (hero). (Hero) was always chosen for everything, while ( enemy) was never chosen. (Enemy) did not appreciate this. When the two brothers grew up, (hero) had been chosen to be the planet protector. This made (enemy) very mad. After the ceremony of (hero) becoming the planet protector, (enemy) went home. He looked it the mirror and yelled at the top of his lungs, "BROTHER, IF YOU WILL BE THE GOOD, I WILL BE THE BAD!" After that, he went to bed. In the morning, he forced 5 people to join the bad side. These people's names were (side hero1), (side hero2), (side hero3), (side hero4), and (side hero5). Then, ( enemy) made a robot army, and made the 5 slaves leaders of the robots. (Enemy)'s new goal is to take over the planet and kill (hero). (Hero)'s goal is to now build a military, and fight back, too save the planet.