The first attempts to create a transcontinental railroad failed in part because

The collapse of the roman empire most likely to empower the catholic church because

Why have some historians rejected the labels bc and ad as laels for periods in world history

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.