“The twentieth century had dispensed with the formal declaration of war and introduced the fifth column, sabotage, cold war, and war by proxy, but that was only the beginning. Summit meetings for disarmament pursued mutual understanding and a balance of power but were also held to learn the strengths and weaknesses of the enemy. The world of the war-or-peace alternative became a world in which war was peace and peace war.”

Address to the Senate (22 January 1917)
1910s
Context: The question upon which the whole future peace and policy of the world depends is this: Is the present war a struggle for a just and secure peace, or only for a new balance of power? If it be only a struggle for a new balance of power, who will guarantee, who can guarantee, the stable equilibrium of the new arrangement? Only a tranquil Europe can be a stable Europe. There must be, not a balance of power, but a community of power; not organized rivalries, but an organized common peace.

Sometimes erroneously prepended to the opening line "The art of war is of vital importance to the State", but appears to be a variation of the Roman motto "Si vis pacem, para bellum". It's not clear who first misattributed this phrase to Sun Tzu. The earliest appearance of the phrase in Google Books is 1920, when it appeared in a pharmaceutical journal, but no attribution was given then.
Misattributed

Source: Songs of the Soul (1971)
Context: War forgets peace. Peace forgives war. War is the death of the life human. Peace is the birth of the Life Divine. Our vital passions want war. Our psychic emotions desire peace.

Some Reflections on Peace in Our Time (1950)

The Second Coming (1980)

16 February 2010
Twitter

"EMU and international conflict", 1997

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.

Source: 1984