Answer :
Scyscrapers.
Streetcars made growth of suburbs possible (otherwise people wouldn't settle so far from center, where they were working). Steel and glass had a similar effect on scyscrapers - it made their construction possible.
Streetcars made growth of suburbs possible (otherwise people wouldn't settle so far from center, where they were working). Steel and glass had a similar effect on scyscrapers - it made their construction possible.