There were Greek colonies in Sicily, but these were mostly in the interest of Sparta.  There had been some fighting there in the earlier years of the war, and Alkibiades was very anxious to lead another expedition thither.  Nikias thought this imprudent, and argued much against it; but the effect of his arguments was that the Athenians chose to join him in the command of it with Alkibiades, much against his will, for he was elderly, and out of health, and, of all men in Athens, he most disliked and distrusted Alkibiades.