“To suggest that war can prevent war is a base play on words and a despicable form of warmongering. The objective of any who sincerely believe in peace clearly must be to exhaust every honourable recourse in the effort to save the peace. The world has had ample evidence that war begets only conditions which beget further war.”

Peace on Earth (1987), tr. Elinor Ford (1994) from Pokój na Ziemi, Ch. 2

Free Speech in Wartime (October 6, 1917)

This passage contains some phrases King later used in "Where Do We Go From Here?" (1967) which has a section below.
1950s, Loving Your Enemies (Christmas 1957)
Context: Let us move now from the practical how to the theoretical why: Why should we love our enemies? The first reason is fairly obvious. Returning hate for hate multiplies hate, adding deeper darkness to a night already devoid of stars. Darkness cannot drive out darkness; only light can do that. Hate cannot drive out hate; only love can do that. Hate multiplies hate, violence multiplies violence, and toughness multiplies toughness in a descending spiral of destruction. So when Jesus says "love your enemies," he is setting forth a profound and ultimately inescapable admonition. Have we not come to such an impasse in the modern world that we must love our enemies-or else? The chain reaction of evil-Hate begetting hate, wars producing more wars-must be broken, or we shall be plunged into the dark abyss of annihilation.

…sogar daß ihm auch wohl Philosophen, als einer gewissen Veredelung der Menschheit, eine Lobrede halten, uneingedenk des Ausspruchs jenes Griechen: »Der Krieg ist darin schlimm, daß er mehr böse Leute macht, als er deren wegnimmt«.
As quoted in Philosophical Perspectives on Peace: An Anthology of Classical and Modern Sources (1987) by Howard P. Kainz, p. 81
Eternal Peace (1795)

A remark to his private secretary, Lord Sandon, in May 1919. From Terence H. O'Brien, Milner, Viscount Milner of St James and Cape Town 1954-1925, 1979, Constable, p. 335.

Speech to the US Congress (26 July 1994)
Context: I, serial number 30743, Lieutenant General in reserves Yitzhak Rabin, a soldier in the Israeli Defense Forces and in the army of peace, I, who have sent armies into fire and soldiers to their death, say today: We sail onto a war which has no casualties, no wounded, no blood nor suffering. It is the only war which is a pleasure to participate in — the war for peace.

"Ceremony of the Innocent: A novel", first edition Doubleday, 1976, p. 218
1970s-

Source: The Ways and Power of Love (1954), p. xi

This attributed to Sun Tzu and his book The Art of War. Actually James Clavell’s foreword in The Art of War http://www.scribd.com/doc/42222505/The-Art-Of-War states http://www.collegetermpapers.com/TermPapers/History_Other/Sun_Tzu_vs_The_Wisdom_of_the_Desert.shtml, “’the true object of war is peace.’” Therefore the quote is stated by James Clavell, but the true origin of Clavell's quotation is unclear. Nonetheless the essence of the quote, that a long war exhausts a state and therefore ultimately seeking peace is in the interest of the warring state, is true, as Sun Tzu in Chapter II Waging Wars says that "There is no instance of a country having benefited from prolonged warfare. It is only one who is thoroughly acquainted with the evils of war that can thoroughly understand the profitable way of carrying it on." This has been interpreted by Lionel Giles http://www.dutchjoens.info/SunTzu%20-%20Art%20of%20War.pdf as "Only one who knows the disastrous effects of a long war can realize the supreme importance of rapidity in bringing it to a close."
Dr. Hiroshi Hatanaka, President of Kobe College, Nishinomiya, Hyōgo, Japan is recorded as saying "the real objective of war is peace" in Pacific Stars and Stripes Ryukyu Edition, Tokyo, Japan (10 February 1949), Page 2, Column 2.
Misattributed