For your race, in its poverty, has unquestionably one really effective weapon — laughter. Power, money, persuasion, supplication, persecution — these can lift at a colossal humbug — push it a little — weaken it a little, century by century; but only laughter can blow it to rags and atoms at a blast. Against the assault of laughter nothing can stand. You are always fussing and fighting with your other weapons. Do you ever use that one? No; you leave it lying rusting. As a race, do you ever use it at all? No; you lack sense and the courage.

Mark Twain (1835-1910) American writer [pseud. of Samuel Clemens]

Story (1916), The Mysterious Stranger, ch. 10
    (Source)

Satan speaking. Often paraphrased: "The human race has one really effective weapon, and that is laughter."

The novella was published posthumously (and with significant alterations by Twain's executor).

The above is taken from the Paine-Duneka text. An earlier version (of this story and passage) appear in The Chronicle of Young Satan, ch. 10 (c. 1898-12):

For your race, in its poverty, has unquestionably one really effective weapon -- laughter. Power, Money, Persuasion, Supplication, Persecution -- these can lift at a colossal humbug, -- push it a little -- crowd it a little -- weaken it a little, century by century: but only Laughter can blow it to rags and atoms at a blast. Against the assault of Laughter nothing can stand. You are always fussing and fighting with your other weapons: do you ever use that one? No, you leave it lying rusting. As a race, do you ever use it at all? No -- you lack sense and the courage.