Beside steel, what was the other breakthrough that allowed buildings to grow so tall?

Elevators and lack of city space.  Since there was less real estate available on land, they had no other choice but to build upwards.  

wood carving remains today the primary sculptural art form of the sub saharan continent. african art history shows the earliest wooden sculptures from the 17th c are attributed to the kuba, central zaire but the earliest surviving sub-saharan sculpture is a zoomorphic head found in 1928 in central angola.

i hope this .

(e) a major consequence of the election was that several southern states