By the middle of the decade, various trends were vying for popular success. Sly & the Family Stone's pop-funk had spawned singers like Roberta Flack and Donny Hathaway, alongside George Clinton's spacy P Funk extravaganzas, Lynyrd Skynyrd and the Allman Brothers Band led a wave of country rock bands. Pop progressive-hard rock bands like Boston, Kansas, Journey, and Styx had long-running popularity. Bruce Springsteen garnered critical acclaim during much of the decade, finally breaking through in a big way very late in the 1970s. Disco, especially The Bee Gees and Donna Summer, were dominating the charts the last few years of the decade, while punk rock and other genres were developing underground.