Complex sentence: Hard bop was developed in the mid- 1950s, coalescing in 1953 and 1954; it developed partly in response to the vogue for cool jazz in the early 1950s, and paralleled the rise of rhythm and blues.
Split into simpler sentences: Hard bop was developed in the mid- 1950s, partly in response to the vogue for cool jazz in the early 1950s. The hard bop style coalesced in 1953 and 1954, paralleling the rise of rhythm and blues.