Which transportation development had the greatest long-term impact on the american economy

Why was the treaty of versailles harsh on germany?

What country was the philippines declaring independence from in this proclamation?

The rise of advertising in the 1920s. i am good with seeing how advertisements shape the roaring twenties and how it developed a new way of life through modern days. but i am not sure what the details of advertising in the 1920s were. if possible can you send me links (preferrably credential links) to sources that maybe show like the first company to start advertising through the radio, how advertising benefits (statistics graphs), etc.