Ender wass motivated to save the world purely by force and a desire to have his life back. He was forced to undergo training at battle school and had to leave his family. The rest of his life now rested in somebody else's hands now not his. He had nothing he could do about his life just like Mazer Rackham. But when he saw a chance to get his life back Ender immediatly took action. He rebelled against the rules and killied the buggers in the supposed video game but turns out it was actually real and he did destroy the buggers.
The buggers motivation was to take over the planet and expand their colony. The humans mistook this and thought the bugger were planning an invasion which led a full-fledged war which ended with the bugger population completely wiped out.
The climax is when Ender is brought to the simulator, with several commanders watching, and told by Mazer that this is his final test. As the simulation starts, Ender finds his human fleet far-outnumbered by the Bugger forces above a planet. Despite being told that it was against the rules, Ender sacrifices most of his fighters fleet to launch a Molecular Disruption Device at the planet, destroying the planet and the entire Formic fleet. Though Ender had anticipated that breaking the rules would mean he would be Kicked out from school, he discovers the commanders celebrating and cheering. Mazer returns, and tellsEnder that this was not a simulation, but the actual thing and the Formic main fleet at the Formic homeworld, Ender has just destroyed the Formic homeworld and killed the Formics, ending the war.
Person vs Person
Ender is in many conflicts with people including Stilson, a bully from preschool, Peter, his cruel brother and bully, and Bonzo, a jealous salamander team commander who ended up trying to kill Ender.
Person vs Society
Ender did not want to kill the Buggers but the society or the commanders and officer of the space programs and government wanted him to. They eventually won and Ender demolished the Buggers.
Somebody, Wanted, But, So Summary
The commanders wanted Ender to destroy the Buggers and end the war But Ender did not want to destroy them because he knew they were innocent so he tried rebelling against the commanders, breaking the rules and trying to get kicked out of command school.