The development of mass communication technologies and the economical growth in the US.
The newspaper advertising came to America later than to Europe, where newspapers were initially invented.
The first American newspaper was printed in 1704 in Boston. It was called "The Boston Newsletter" and contained some announcements about the reward, offered for catching a thief of some male clothes. When the US became a country, there were about thirty local newspapers with news info and some ads, which now we would call the classified local advertising.
From 1870 to 1900, these three decades had the greatest influence and were of great importance to the advertising progress in the US.
In a very short frame of time, the USA turned from an agricultural country with the European ways of marketing traditions, the system of product distribution and the promotion into a great industrial country with totally new ways of the product promotion and distribution.
Advertising entered a new age in its history.
The development of the transportation system was a very important influence on the advertising progress. The US is about 3000 miles wide. This is a rich land of the nature, fertile soil, forests and coal mines. At first, the transportation was all bound to the rivers and people traveled and transported goods only by boats.
Consequently, with the development of the railway network, people started to explore new lands and, accordingly, to produce and transport more goods.