Here’s a provisional timeline—I’ll add to it as I go…
1991 — Billboard magazine starts using SoundScan to track record sales. Rap, metal, and country are selling far more than record execs initially thought, so they start diverting resources to those kinds of artists. It also allows for targeted marketing of new artists and new releases. This was around the time that west-coast rap was gaining mainstream attention with artists like N.W.A. and Ice-T.
1991-1995 — The beef between east coast and west coast rappers unfolded, with Biggie, Puff Daddy and Bad Boy representing the former and Tupac, Suge Knight and Death Row representing the latter. Southern rap emerged onto the national scene with groups like OutKast, who famously announced at the 1995 Source Awards that “the South got something to say.”
1996 — Telecommunications Act deregulates the number of media properties that any one entity can own, leading to the rise of media monopolies like ClearChannel. This paves the way for a consolidation of mainstream media outlets, a rise in “megastars,” and a homogenization of sounds (i.e., rap = gangsta rap). Also worth mentioning that the mainstream rap media was dominated by monthly glossy magazines like VIBE, The Source, and XXL. But SOHH.com (Support Online Hip Hop), one of the first websites devoted to rap music, was launched by Felicia Palmer and Steven Samuel.
1999 — The peer-to-peer file sharing program Napster launches and facilitates easy and free access to an awful lot of music. The recording industry is not pleased. They sue Napster and it ceases operations in 2001. LimeWire, a similar service, appeared in 2000. There’s an important shift that happens here (and with respect to the launch of the iTunes store referenced below) about the shift from physical media to virtual media.
2003 — Apple launches the iTunes store, with a large catalog of music from the major labels available to download for 99 cents.
2005 — Eskay starts nahright.com, one of the landmark blogs of the blog era. The mixtape distribution site DatPiff launches.
2007 — DJ Drama’s studio [?] is raided by the FBI and his mixtape operation is shut down. Later that year Soulja Boy releases the song “Crank That (Soulja Boy) via YouTube. The video which featured the dance, became a viral sensation. The website Hot New Hip Hop comes online.
2008 — Barack Obama becomes the first Black president of the United States. Many scholars point to this as the moment that our society became “post-racial”; that is, free from race-based decision-making, remedies, or exclusion.
2016 — Music streaming revenue eclipses digital download revenue for the first time.