Defence Confederation

Harriet Riddle: “I thought about it, more of a name that didn’t inform everyone what we were doing, so we can discuss it in a safe manner outside meetings.”

Cho Chang: “''The Defence Association? The D.A. for short, so nobody knows what we’re talking about?''”

Ginny Weasley: “Yeah, the D.A.’s good, only let’s make it stand for Dumbledore’s Army because that’s the Ministry’s worst fear, isn’t it?”

Harriet Riddle: “Hah!”

Ginny Weasley: “What?”

Harriet Riddle: “That’s a terrible name, ‘Dumbledore’s Army’ is the best way to get caught!”

Ginny Weasley: “That’s what referring to it as ‘D.A.’ is for.”

Harriet Riddle: “''Also, Ginny, that attempt to one-up Cho was so pathetic it almost made me laugh -- almost; Cho’s idea actually had some decency. Thank you, Cho, for that marvelous suggestion now, that gave me an idea! Defence Confederation! For short we can pretend we're talking about Washington D.C.”''

— The creation of the group's name

Defence Confedration (also known as the D.C.) was a secret organisation initiated by Harry Potter and Harriet Riddle, to teach their fellow Hogwarts colleagues proper Defence Against the Dark Arts in 1995. It was founded by Harriet Riddle, and led by her and Harry, who also had the responsibility of teaching its members.

This organisation was made essential by the rejection of Dolores Umbridge, the subject's professor during the 1995-1996 school year, to teach anything in her classes other than textbook theory. It was initially founded with twenty-eight members. The group was disbanded during the 1996-1997 school year following the selection of Severus Snape as Defence Against the Dark Arts teacher, even though several members regarded the call and took part in the Battle of the Astronomy Tower at the end of the year.

Formation
Harriet Riddle: "Harry, don't you see? This... this is exactly why we need you... We need to know what it's really like... facing him... facing V-Voldemort. Well ... think about it. Please?"

Harry Potter: "But it's you they need, not me you!"

Harriet Riddle: "HARRY THAT'S IT! YOU'RE A GENIUES! We'll both lead!"

Harriet Riddle persuading Harry Potter to teach practical defence.

Soon after their fifth Defence Against the Dark Arts lesson during their fifth year, it soon became clear to Harry Potter and Harriet Riddle that practical defensive magic would not be taught in the class. Instead, under the management of Dolores Umbridge, a Ministry-approved curriculum of philosophy only would be used to teach. Minister for Magic Cornelius Fudge was scared that Albus Dumbledore could use useful lessons to train an army of wizards and witches to oppose him and to try to take over the Ministry, since he refused to believe that Lord Voldemort had returned. They claimed that it was “trauma” from the Triwizard Tournament.

Worried that they needed defensive magical skills to combat Voldemort and his Death Eaters, Harriet proposed the formation of a practical study group to be taught by Harry. Harry was initially reluctant but, wanting Harriet to teacher, and Harriet realised they would both teachers. Harriet arranged a meeting in the Hog's Head during the first Hogsmeade visit of the school year for anyone who wanted to learn, although Harry was doubtful that anyone would turn up. Since the Daily Prophet had started a slander against him, several of the students deemed him to be either a fraudster or crazy.

"I-I think everybody should write their name down, just so we know who was here. But I also think that we all ought to agree not to shout about what we’re doing. So if you sign, you’re agreeing not to tell Umbridge — or anybody else — what we’re up to"

— Harriet Riddle regarding the importance of group membership and secrecy.