What , according to pinchot , is the " first principle of conservation "?

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.

What are some effects outside of europe because of world war 1?

Describe how the ways in which african americans migrated during the great migration were similar to the immigrants who arrived from other countries in the early 1900s.