Every decade takes a couple of years to feel like itself, but the 1990s, in particular, had a soft launch. While 1991 would bring a bumper crop of era-defining albums from the likes of Nirvana, Pearl Jam, U2, and Red Hot Chili Peppers that would set the tone for alternative rock for the rest of the decade, the music of 1990 often feels like an outgrowth of the previous decades. Even the year’s biggest rock debut that was positioned as a contrast from hair metal was the decidedly retro Black Crowes. Billboard’s Modern Rock chart, which had just been launched in late 1988, was still dominated by established British bands like The Psychedelic Furs and Gene Loves Jezebel. Depeche Mode and Sinead O’Connor became the year’s unlikely crossover stars. Observe the chart in the last week of&nb...