Well, we have read and loved many of the books already mentioned in this thread but I’m going to try to think of some titles that focus on key events and people in American history for someone who wants to hit the highlights.
If you are specifically wanting Landmark books, I would pick one on George Washington, John Adams, and one overview of the American Revolution.
The Landing of the Pilgrims would be a great one to cover the beginnings of American colonization.
Abraham Lincoln: Log Cabin to White House is excellent.
I would follow that one up with an overview of the Civil War.
A couple of good books on America’s involvement in the World Wars would be good to round out American in the modern age.
I also want to recommend a set of excellent narrative American history books that we have really enjoyed. If you chose these books, they would give a great overview of all American history. They are the history for Peter series by Gerald Johnson. I can’t recommend them highly enough! They are written at about the same level as most Landmark books, are not overwhelming in size, and are extremely well written.
I didn’t recommend specific Landmark titles for the most part, because we read so many that I can’t remember the exact titles other than the Abe Lincoln book.