What are the major events of Ender's Game?
The first major event in Ender's Game is Ender's decision to go to Battle School. He is a virtual pariah at home, bullied by other boys, and in danger from his sadistic older brother. He leaves his family partly because he wants to be safe, partly because he wants to keep his sister safe, and partly because that was his role as a "Third" child in the future society.
The second major event occurs when Ender starts to make independent decisions that overrule his Battle School commander; his military mind is better in zero-gravity and he becomes the leader of his own army group. His success is resented by others, but he is able to continue winning battles, even with a group of new recruits with no experience.
The third major event comes after Ender has graduated and tried to leave the military behind; he is convinced to go into training to fight the "Buggers," insectoid aliens, to help keep humanity alive. His commander does not tell him that his final simulated battle is, in fact, real, and using the tactics and military intelligence he gained from all his training he destroys the Bugger homeworld, an event that leaves him traumatized.
The final major event comes when Ender discovers a final Bugger queen egg on one of their colony worlds. Struck by the pain of his actions and the knowledge that he had no other choice to save humanity, Ender vows to continue searching for a homeworld for the extinct species, and a religion forms around his writings.