Different Eras of R&B

In the 1920s and 1930s, the migration of African Americans to the urban industrial centers and elsewhere created a new market for jazz, blues, and related genres of music, often performed by full-time musicians, either working alone or in small groups. There was increasing emphasis on the use of electric guitars a lead instrument, including the piano and saxophone. In the 1930s, Louis Jordan’s small combo started making blues-based records with humorous lyrics and upbeat rhythms that owed as much to boogie-woogie as to classic blues forms. Jordan's band, the Tympany Five formed in 1938, had him on both sax and vocals with accompanying musicians on trumpets, tenor saxophones, a piano, bass, and drums.  This music, sometimes called jump blues, set a pattern that became the dominant black popular music form during and for some time after World War II.

In 1949, the term rhythm and blues replaced the Billboard category Harlem Hit Parade and in the same year, "The Huckle-Buck", recorded by band leader and saxophonist Paul Williams, was the No.1 R&B tune, remaining on top of the charts for nearly the entire year.  In 1949, the latest version of a 1920s blues song, "Ain't Nobody's Business" was a No.4 hit for Jimmy Witherspoon, and Louis Jordan and the Tymphany Five once again made the top 5 with "Saturday Night Fish Fry". Several of these hit records were gradually issued on new independent record labels, such as Savoy (1942), King (1943), Imperial (1945), Specialty (1946), Chess (1947), and Atlantic (1948).

In 1951, working with African American musicians, Greek American Johnny Otis scored ten top ten R&B hits, including: "Double crossing blues", "Mistrustin' blues" and "Cupid's Boogie", all of which hit No.1 that year. In July 1951, Cleveland, Ohio DJ Alan Freed started a late-night radio show called "The Moondog Rock Roll House Party" on WJW-AM (850). Ray Charles came to national celebrity in 1955 with "I Got a Woman". It was an upfront use of gospel music conventions in an R&B background.
In 1956, an R&B "Top Stars of '56" tour took place, with headliners Al Hibbler, Frankie Lymon and the Teenagers, and Carl Perkins, whose "Blue Suede Shoes" was very popular with R&B music buyers. The tour visited Columbia, SC, Annapolis, MD, Pittsburgh, PA, Syracuse, Rochester and Buffalo, NY, into Canada, and through the mid Western US ending in Texas. There was numerous rioting going on, just crazy, man! The music drove 'em insane." In Annapolis 70,000 to 50,000 people tried to attend a sold out performance with 8,000 seats. Roads were blocked for seven hours. Film makers took advantage of the popularity of "rhythm and blues" musicians as "rock n roll" musicians beginning in 1956.

Before 1960s, the music industry group is known as rhythm & blues was called soul music, & similar music by white artists was labeled blue eyed soul. In 1960 R&B performers like Washington, Charles, & Ruth Brown were appearing more in nightclubs than in the multi performer revues in which they had made their names. Young performers like Jackie Wilson & Sam Cooke owed a debt to the earlier rhythm & blues performers. They were more transitional figures who were, like Charles, establishing the new genre of soul.
In 1961, Stax Records introduced Memphis soul with the Mar-Keys' "Last Night", an instrumental featuring built around horns, electric organ, and drums. 

By the early 1970s, soul music had been influenced by psychedelic rock and other genres. By the end of the 1970s, disco and funk were dominating the charts. At that period, previous Rhythm & Blues was an influence on British pub rock & later, the mod revival. At that time the term R&B is always used instead of the full rhythm & blues, & mainstream use of the term generally refers to Contemporary R&B, which is a newer version of soul & funk influenced pop music that originated as disco faded from popularity.
In the mid of 1980s, the transition from soul & disco to R&B, new stars like Prince & Michael Jackson rose in popularity.  A popular, but short lived group with more pronounced R&B roots was Levert.
After 2000s, the cross pollination between R&B & hip hop had increased. R&B began to focus more on solo artists rather than groups as the 2000s progressed. But soulful R&B continues to be popular. Now-a-days a band that advertises itself as rhythm & blues is undoubtedly following in this tradition rather than that of the early pioneers.