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.  

you will need these

an outline of all three paragraphsan identification of the historical era that you are writing aboutan explanation of the term mass productiona description of two ways new technology affected industrya conclusion that shows how new technologies allowed industrialization to grow