In researching strategies to beat Voldemort, Harry notices that most magical warfare in recent years has been fought by comparatively small groups in smaller skirmishes and very few pitched battles. He brings his findings to Hermione, and they modify the DA to train students to fight in groups as small, mobile squads. Group sizes range from pairs to as many as 16-20 people.
The result of all of this training is that when the war finally does break out, the portion of the student body that participated in the DA become inexplicably good at keeping the Hogwarts grounds a safe haven for any resistance to Voldemort. After passing on their training to others, nearly every person who took shelter at Hogwarts is now bringing the fight to the Death Eaters.
The war goes much more favorably for the good guys, and as Harry, Hermione, and Ron take out more of the horcruxes, the Death Eaters start taking mounting losses. The end result is a laughably easy fight for Harry after he gets the horcrux out of himself.
Now that people are more ready to stand up for themselves, Harry feels more comfortable leaving Britain with his now girlfriend, Hermione, to explore the world.
@novice-at-everything
