A. We've known for years there's corruption in video game journalism. We've had reviewers admit companies can demand good reviews, and bad reviews can get reviewers fired. The News sites get their money from advertisements, which are for games, which are meant to be reviewed neutrally. It's a bad arrangement, and people have been getting angry.
B. As video games grow in popularity and move into new markets and demographics, we're seeing new types of game, and we're seeing games get criticized for things that weren't traditionally on the minds of reviewers, like diversity in the cast, how the characters dress and are written, etc. That's fueled resentment from people enjoying the games. This has gotten very heated due to the criticisms being a mix of good points and genuinely ignorant nonsense.
C. Some months ago, developer Zoe Quinn claims to have been the target of a harassment campaign. Those she accused claim she is lying trying to get publicity for her work. She has no solid proof this happened, nor is there particularly good evidence it didn't. It's essentially "he says, she says".Here's the Gamergate timeline, adapted from a summary by Sorcan.
1. Zoe Quinn is accused of sabotaging The Fine Young Capitalists' charity event with feminism as her justification, even though the event supposedly aimed to support female developers. She maintains their rules were exclusionary to transsexuals, they maintain they needed to be precise in their rules for legal reasons. Initially The Fine Young Capitalists claim that she personally attacked their site. They have since stated they think the attack came from a supporter of hers, who may have taken the initiative without being asked.
2. A more or less reasonable group of people get upset about this, and make the issue somewhat known.
3. Zoe's ex-boyfriend shares information about their sex life, which picks up popularity because of allegations that she had slept with video game reviewers for good reviews. Evidence to prove/disprove that allegation is muddy at best.
4. The allegations begin to get larger. The resentment toward corruption in the industry comes into play. People maintain that not only are the claims true, but that the problem is widespread, with reviewers and a clique of certain developers trying to manipulate the indie game industry, deciding who gets to be popular and who doesn't. It's called a conspiracy by some (although people who believe it start embracing the name "Quinnspiracy")
5. Extremists on both sides do their thing, ie. making lives miserable. There's large scale harassment (some of it absolutely misogynistic), and there's people claiming that anyone critical of Zoe and the reviewers must be a misogynist (which is absurd).
6. News sites, always eager to paint things in black and white, ignore the concerns raised by the reasonable people and make the issue about feminism versus misogyny, grouping all people who don't praise the woman in the latter category. (With the exception of some more right-wing news sites, which take the stance that feminists are just out of control)
7. The aforementioned reasonable people, having been lumped together with misogynists, become resentful of news websites who use the "feminism" debate to cover their refusal to address real issues. This adds fuel to the fire, making anyone with reasonable criticisms about the industry actually less likely to be bothered by extremists on their side (especially when they find themselves under attack by websites they used to enjoy).
8. An unusually high number of comments, videos, and forums posts are deleted en masse for siding with "gamersgate", regardless of whether they were reasonable, extremist, or downright misogynistic. Everyone got painted with the same brush.
9. A portion of the reasonable people begin thinking there's maybe something to this whole "conspiracy" angle, and start becoming indistinguishable from the extremists.
10. Repeat steps 7, 8, and 10 until the whole world's gone crazy and everybody on one side is convinced that everybody on the other side is a mis[ogyn/andr]ist, while everyone on the other side is convinced that there are absolutely no mis[andr/ogyn]ists on their "side".
11. Brietbart "blows the whole thing open" by revealing secret emails showing that reviewers for video game news sites asked one another for advice on how to handle the allegations about Quinn, since they felt this was newsworthy stuff but were reluctant to make the situation worse. This is taken by some as proof that reviewers regularly contact one another to decide what to cover, in an attempt to decide the shape of the industry.
12. Armageddon (presumably)