The second industrial revolution refers to the changes in manufacturing and building, and the new inventions brought about by the introduction of inexpensive steel. After the Second Industrial Revolution cites were overcrowded because of the need of jobs for people. The streets of cities were overcrowded which had sanitation issues so, lots of people were getting sick as a result. Crime grew as a result of not enough police and because it was easy to lose the police in crowds of people. Devices such as cars, electric lights, and telephones made the middle class's life more enjoyable. People who did urban planning reforms such as trolly parks made it so the working class could spend their extra time and money on something enjoyable.