"Manifest Destiny was the belief widely held by Americans in the 19th century that the United States was destined to expand across the continent. The concept, born out of 'a sense of mission to redeem the Old World', was enabled by 'the potentialities of a new earth for building a new heaven.'" (Wikipedia, citing Frederick Merk)
Now, Michael Porath has told the story of manifest destiny in a series of 141 maps. The main technical trick is that Porath designed the site in HTML5, so it has some nice interactive features. The maps appear on a single page in four columns but you can click any of them for a close-up with an explanation of the changes, or mouse-over a region of the map to see what political entity it was under at the time (e.g. unorganized territory, Spanish colony).
There are two additions that I think would help improve this project. The first is a sense of time scale--some of the maps are only a month apart (January and February 1861, for example) while others are separated by several decades (March 1921 and January 1959). Adding time would allow for a second feature: an animation that would show the areas of change and continuity over time. An excellent example of this is David Sparks' choropleth maps of presidential voting over time. I do not know whether this could still be done in Porath's HTML5 setup, but it is often useful to think about changes to graphical displays (additions or subtractions) that would help to convey meaningful information. What other suggestions do you have for these maps?