… is from page 249 of Speeches on Questions of Public Policy by Richard Cobden, James E. Thorold Rogers, ed.; specifically, it’s from a speech delivered on January 10, 1849 by Cobden to the people of Manchester:
It is of paramount moment to the English people that we should not allow ourselves to entertain an undue or exaggerated notion of our own importance as a nation, or to take a too unfavourable view of other countries. It is through your national pride that cunning people manage to extract taxes from you. They persuade you that nothing can be done abroad unless you do it; and that you are so superior to all other countries, that your next neighbour, France, for instance, is nothing but a band of brigands, and unless you are constantly on the watch, they will be ready to pounce upon you and carry off your property.