“In peace, prepare for war. In war, prepare for 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
“The true objective of war is peace.”
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." <br class="br">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. <br class="br">Misattributed
Variant: Thus it is that in war the victorious strategist only seeks battle after the victory has been won, whereas he who is destined to defeat first fights and afterwards looks for victory.
Source: The Art of War, Chapter IV · Disposition of the Army
“The art of war is of vital importance to the State.”
Sun Tzu book The Art of War
The Art of War, Chapter I · Detail Assessment and Planning
Context: The art of war is of vital importance to the State. It is a matter of life and death, a road either to safety or to ruin. Hence it is a subject of inquiry which can on no account be neglected.
Variant translations
It is best to keep one’s own state intact; to crush the enemy’s state is only second best.
Source: The Art of War, Chapter III · Strategic Attack
“What is essential in war is victory, not prolonged operations.”
Source: The Art of War, Chapter II · Waging War
Source: The Art of War, Chapter VIII · Variations and Adaptability
“In war, numbers alone confer no advantage. Do not advance relying on sheer military power.”
Source: The Art of War, Chapter IX · Movement and Development of Troops
“Secret operations are essential in war; upon them the army relies to make its every move.”
Source: The Art of War, Chapter XIII · Intelligence and Espionage
“Thus, what is of supreme importance in war is to attack the enemy's strategy.”
Sun Tzu book The Art of War
是故上攻伐谋
The Art of War, Chapter III · Strategic Attack
Variant: Thus, what is of supreme importance in war is to attack the enemy's strategy.
Source: The Art of War, Chapter VI · Weaknesses and Strengths
Sun Tzu book The Art of War
(zh-TW) 孫子曰：國之上下，死生之地，存亡之道，不可不察也。
The Art of War, Chapter 1 · Detail Assessment and Planning
Source: The Art of War, Chapter XI · The Nine Battlegrounds