From site:

A Biography of America is a telecourse and video series that presents American history as a living narrative. This series web site lets you delve further into the topics of the 26 video programs.

From site: American Journeys contains more than 18,000 pages of eyewitness accounts of North American exploration, from the sagas of Vikings in Canada in AD1000 to the diaries of mountain men in the Rockies 800 years later. 

Read the words of explorers, Indians, missionaries, traders and settlers as they lived through the founding moments of American history…

LearningReviews.com note:   This is an excellent place to find primary source documents.

From site:  Conceived in 1993, and online since 1998, Discovering Lewis & Clark is a hyperhistory in progress.  It is enhanced by an average of at least one new interpretive episode each month, employing a variety of multimedia techniques.  The site focuses on issues, values, discoveries and events relating to the Lewis & Clark Expedition, its preludes, and its aftermath to the present time…

Discover Lewis and Clark offers a day-by-day diary, maps, and background on dozens of Native American tribes along their route. The site goes in-depth on several topics related to their expedition, such as medicine, food, music, the fur trade, and boats used.

Use the interactive map to learn more about the history of the 13 original colonies of the U.S.  There are several interactive games and quizzes to help you remember important ideas and dates.  Additional premium features are available for a fee.

Mr. Nussbaum Explorers is an interactive site with profiles of 22 explorers of the Americas. Other sections include: pirates, legends and myths, a summary of the Age of Exploration, Lewis and Clark, Marco Polo and the Silk Road, and an interactive scavenger hunt.

Sections with teacher resources include printables and reading comprehension multiple choice questions.

My observation is that some of the reading materials score at a higher grade level than what is recommended on the site. Also, you may encounter pop-up ads that block content until they are dismissed. The site has posted a notice that it is revamping layout and ads in 2018.