Western tribes exchanged what with explorers?

The chinese exclusion act was the first significant law restricting immigration into the united states. why do you think the us government singled out chinese immigrants in particular for exclusion?

What specific events led richard nixon to resign the presidency

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.