What sparked the term 'Uncle Sam' for the United States?

Uhmm..SSssaaam. <x}
A man named Sam.
Samuel?
A Mr. Samuel Wilson, or Samuel Adams, or Samuel Fischer. 8/

It is now 2305 eastern
Seems our host is busy

What is the Scarlet Letter, and what does it stand for?

The Scarlet Letter is a punishment for adulterers in the Puritan community, where they have to have a red A sewn onto all out of their outerwear, showing their shame
There's also a book of the same name

The Wizard of Oz was intended to be a political alegory. What were Dorothy's slippers and the Yellow Brick Road supposed to represent? (Double points if you can name the president being criticized and the character representing him.)

Dunno if it's the one you're going for, but the silver slippers were meant to represent the silver backed money, while the Golden Brick Road repped the gold backed money
Silver was seen by the author as better, so the slippers guided Dorothy over the damaged road easily while her companions were stumbling and tripping over the damaged road
I think farmers wanted silver to also keep backing because then the money had more value to them, while city rich people wanted it to be just gold to be better for them? Something to that effect? It's been a while so I can't remember off the top of my head

They became ruby in the movie because ruby looked better than silver in technicolor
And if you look closely you can see that she isn't actually always wearing them, but rather a pair of brown shoes