“Far from being a sum of distinct and partial results, victory is the consequence of efforts, some of which are victorious while others appear to be fruitless, which nevertheless all aim at a common goal, all drive at a common result: namely, at a decision, a conclusion which alone can provide victory.”

1970s, Remarks on Being Reelected (1972)

Speech in the House of Commons, after taking office as Prime Minister (13 May 1940) This has often been misquoted in the form: "I have nothing to offer but blood, sweat and tears ..."
The Official Report, House of Commons (5th Series), 13 May 1940, vol. 360, c. 1502. Audio records of the speech do spare out the "It is" before the in the beginning of the "Victory"-Part.
The Second World War (1939–1945)
Context: You ask, what is our policy? I will say: It is to wage war, by sea, land and air, with all our might and with all the strength that God can give us: to wage war against a monstrous tyranny, never surpassed in the dark, lamentable catalogue of human crime. That is our policy. You ask, what is our aim? I can answer in one word: It is victory, victory at all costs, victory in spite of all terror, victory, however long and hard the road may be; for without victory, there is no survival.
Context: I would say to the House, as I said to those who have joined this Government: 'I have nothing to offer but blood, toil, tears, and sweat.' We have before us an ordeal of the most grievous kind. We have before us many, many long months of struggle and of suffering. You ask, what is our policy? I will say: It is to wage war, by sea, land and air, with all our might and with all the strength that God can give us: to wage war against a monstrous tyranny, never surpassed in the dark, lamentable catalogue of human crime. That is our policy. You ask, what is our aim? I can answer in one word: It is victory, victory at all costs, victory in spite of all terror, victory, however long and hard the road may be; for without victory, there is no survival.

Speech to the Empire Rally of Youth at the Royal Albert Hall (18 May 1937), quoted in Service of Our Lives (1937), pp. 162-163.
1937
Context: The twenty post-War years have shown that war does not settle the account. There is a balance brought forward. When emancipation is achieved a new slavery may begin. The moment of victory may be the beginning of defeat. The days which saw the framing of the League of Nations saw the signing of the Treaty of Versailles. Should both be entered on the credit side? Twenty years ago we should all have said, "Yes"; to-day the reply would be doubtful, for both have belied the hopes of mankind and given place to disillusion. Freedom for common men, which was to have been the fruit of victory, is once more in jeopardy in our own land because it has been taken away from the common men of other lands.

1990s, Long Walk to Freedom (1995)

Source: Report on the Potsdam Conference (1945)
Context: Our victory in Europe was more than a victory of arms.
It was a victory of one way of life over another. It was a victory of an ideal founded on the rights of the common man, on the dignity of the human being, on the conception of the State as the servant — and not the master — of its people.
A free people showed that it was able to defeat professional soldiers whose only moral arms were obedience and the worship of force.
We tell ourselves that we have emerged from this war the most powerful nation in the world — the most powerful nation, perhaps, in all history. That is true, but not in the sense some of us believe it to be true.
The war has shown us that we have tremendous resources to make all the materials for war. It has shown us that we have skillful workers and managers and able generals, and a brave people capable of bearing arms.
All these things we knew before.
The new thing — the thing which we had not known — the thing we have learned now and should never forget, is this: that a society of self-governing men is more powerful, more enduring, more creative than any other kind of society, however disciplined, however centralized.

Although under a heavy fire for several continuous hours I received only one wound, the breaking of the longest finger of my left hand; but the doctor says the finger may be saved. It was broken about midway between the hand and knuckle, the ball passing on the side next to the forefinger. Had it struck the centre, I should have lost the finger. My horse was wounded, but not killed. Your coat got an ugly wound near the hip, but my servant, who is very handy, has so far repaired it that it doesn't show very much. My preservation was entirely due, as was the glorious victory, to our God, to whom be all the honor, praise, and glory. The battle was the hardest that I have ever been in, but not near so hot in its fire.
Letter to his wife after the First Battle of Bull Run (22 July 1861); as quoted in Memoirs of Stonewall Jackson by His Widow Mary Anna Jackson (1895) http://books.google.com/books?id=bG2vg5cH004C, Ch. XI : The First Battle of Manassas, p. 178

Statement to Woodrow Wilson at the Paris Peace Conference (12 January 1919), as quoted in The Macmillan Dictionary of Political Quotations (1993) by Lewis D. Eigen and Jonathan Paul Siegel, p. 689
Prime Minister

Source: The Art of War, Chapter X · Terrain

Though widely attributed to Herodotus this in fact comes from the Histories of Polybius, Book 16, chapter 28: "Some men, like bad runners in the stadium, abandon their purposes when close to the goal; while it is at that particular point, more than at any other, that others secure the victory over their rivals". (Translation of Evelyn S Shuckburgh).
Misattributed