Here are a few more, Arianne:

"The Dervish and the Offensive Stranger"
"The Czar's Sililoquy"
"King Leopold's Sililoquy: A Defense of His Congo Rule"

I'd also suggest a still-(painfully)relevant discussion point excerpted
below from Jim Zwick's Confronting Imperialism:Essays on Mark Twain and
the Anti-Imperialist League. 

The U.S. military's use of waterboarding began during the
Philippine-American War. Euphemistically called the "water cure," it was
said to be a form of torture the U.S. military "inherited" from the Spanish.
They had used it since the Inquisition. In his 1902 essay "A Defense of
General Funston," Mark Twain wrote:

Funston's example has bred many imitators, and many ghastly additions to our
history: the torturing of Filipinos by the awful "water-cure," for instance,
to make them confess -- what? Truth? Or lies? How can one know which it is
they are telling? For under unendurable pain a man confesses anything that
is required of him, true or false, and his evidence is worthless.

Mark Twain and other anti-imperialists were protesting the U.S. military's
use of waterboarding and other forms of torture one hundred years before
their recent use in the "war on terror."

Randy Abel
Yantai, China