Most of the wizarding world thought that the end of the second war would come in fire. That there would be a great battle where Harry Potter and Voldemort would face each other and only one would be left standing. They put too much faith on a single young man.
Harry Potter, after the death of Sirius Black, embraced the power that came with the sorrow of his loss. Dumbledore had explained to the frightened young man the often the magic that would normally come on their seventeenth birthday came early when said wizard was faced with extreme emotion. However, the old wizard made a single mistake. He assumed that Harry would be safer staying with the Dursley's, even after Harry had told him of the abuse he suffered at their hands, then staying with a member of the Order of the Phoenix.
No one, not even Dumbledore himself, could have foreseen what happened not long after Harry was escorted to his Aunt and Uncle's house. The two guards on duty, Mrs. Weasley and Mr. Lovegood, never stood a chance against the hordes of Death Eaters that attacked Number Four Privet Drive. Besides the death of the two guards Harry's Aunt Petunia, Uncle Vernon, and his cousin Dudley also were murdered. The number of Death Eaters that died in the backlash of Harry's magic trying to protect his friend's parents reached 67. 67 lives that Harry himself had taken.
One of the Death Eaters that got away was Harry's archrivals father, Lucius Malfoy. Malfoy got away but he would never be able to forget the glowing green eyes of Harry Potter that held so much pain, pain that he himself had gone through. Empathy was never one of Malfoy's strong points but a single look from the boy-who-lived caused him to be in agony. For him this was the last straw. The so called 'Dark Side' had been the reason for such a look in a fifteen year old and Malfoy had done nothing but help cause more. For Draco had only just turned sixteen. And he would never be able to stand seeing such a look in his only heir's eyes. So Malfoy repented to Harry, not Dumbledore, and worked to spy on Voldemort and to cleanse the Ministry of Magic of the Death Eater influence that resided there.
Malfoy was the first ally that Harry Potter gained in the war but he certainly was not the last. Voldemort never saw it coming that his top Death Eaters defected to the side of Harry. The boy-who-lived had his own power base with more allies than Dumbledore could have ever achieved. With the Ministry, Werewolves (thanks to Remus Lupin), Centaurs (Firenze had helped there), Giants (Hagrid turned out to be much more loyal to the boy-who-lived than to Dumbledore), and the numerous Purebloods who had switched sides. It took seven years but in the end, it was Slytherin tactics that brought about the end of the self-proclaimed Dark Lord.
After the death of his mother, Ron Weasley was declared insane and sent to Saint Mungo's. What was left of his sanity was torn apart after one visit from Harry and he tried to extract vengeance on him for his mother's death. This, of course, broke Harry's heart to see his best friend like this.
Luna reacted much better to the news of her father's death than Ron did to that of his mother's. Luna joined Harry in the fight against Voldemort using her knowledge of creatures than no one else knew about. The Nargles and other such creatures turned out to actually exist but very few people could actually see them.
One might think that Hermione joined Harry in the war as a top researcher but that is the exact opposite from the truth. Blinded as she was by her search for knowledge, Hermione fell to the temptation of Dark Magic when she was twenty years old. Her friendship with Harry fell out after Ron and his insanity. She betrayed Harry and it broke his heart even further into pieces to see Hermione fall.
The Weasley's stuck by Dumbledore through everything and they all survived the war. The twins, Bill, and Charlie joined with Harry while their father, sister, and Percy stuck together working for the Ministry.
The twins turned out to be brilliant strategists and came up with the plan the ultimately killed Voldemort. Charlie and his co workers in Romania brought the combined forces of the Romanian Government and the dragons to the side of the boy-who-lived.
The greatest thing that happened to Harry Potter through the years after his godfather's death was his friendship with Draco Malfoy. Draco turned from the snobbish boy that thrived to torment Harry to an understanding young man who tried his best to help people. It was an astonishing transformation but it came too late for much of the Wizarding world. They naively thought that Draco was a spoiled prat who would never change. But Harry, being Harry, saw the difference that his father's defection had made in Draco. The friendship came slowly, with many fights and disagreements. Their friendship changed however when Draco decided that he wanted more. That he wanted Harry and everything that came with him. And Harry agreed. So the friendship turned to love, something that Harry had always wanted but had been denied all his life. Draco turned out to be the one stable thing in his life and what Harry fought for. The relationship that they formed never went public because the Wizarding world would never understand the love that grew between the two young wizards.
Necessary background information. Some things wouldn't make sense later on in the story… Mostly because I don't plan on explaining them… We'll see what happens…