What caused the post ww1 recession

In 1912, the imperial system that had ruled over china for thousands of years

Was the battle of iwo jima over after us troops raised the flag on mt. suribachi?

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.