The Gilded Age and Second Industrial Revolution
The link address is: https://www.khanacademy.org/humanities/ap-us-history/period-6/apush-gilded-age/v/the-gilded-age-part-2
The link address is: https://www.khanacademy.org/humanities/ap-us-history/period-6/apush-gilded-age/v/the-gilded-age-part-2