“Once we have a war there is only one thing to do. It must be won. For defeat brings worse things than any that can ever happen in war.”

"Speech to the Norwegian Storting" (30 March 2022) https://www.president.gov.ua/en/news/promova-prezidenta-ukrayini-volodimira-zelenskogo-v-parlamen-73961

Source: A Farewell to Arms

Report on the Potsdam Conference (1945)
Context: Any man who sees Europe now must realize that victory in a great war is not something you win once and for all, like victory in a ball game. Victory in a great war is something that must be won and kept won. It can be lost after you have won it — if you are careless or negligent or indifferent.
Europe today is hungry. I am not talking about Germans. I am talking about the people of the countries which were overrun and devastated by the Germans, and particularly about the people of Western Europe. Many of them lack clothes and fuel and tools and shelter and raw materials. They lack the means to restore their cities and their factories.
As the winter comes on, the distress will increase. Unless we do what we can to help, we may lose next winter what we won at such terrible cost last spring. Desperate men are liable to destroy the structure of their society to find in the wreckage some substitute for hope. If we let Europe go cold and hungry, we may lose some of the foundations of order on which the hope for worldwide peace must rest.
We must help to the limits of our strength. And we will.

Conversation with Frank Irving Cobb before asking Congress to declare war (2 April 1917). Attributed in Cobb of "The World," a leader of liberalism, by Cobb and Heaton, 1924, p. 270 http://books.google.com/books?id=Vxt5W3LrvSYC&pg=PA270&dq=%22Once+lead+this+people%22
1910s

The Fall of Tobruk, 20 June 1942.
The Second World War, Volume IV : The Hinge of Fate (1951) Chapter XII. pp. 343-4.
The Second World War (1939–1945)

Statement of August 1934, after being expelled from Germany, quoted in Dorothy Thompson : A Legend In Her Time (1973) by Marion K. Sanders, p. 199
Context: As far as I can see, I really was put out of Germany for the crime of blasphemy. … My offense was to think that Hitler is just an ordinary man, after all. This is a crime against the reigning cult in Germany, which says that Mr. Hitler is a Messiah sent by God to save the German people — an old Jewish idea. To question this mystic mission is so heinous that, if you are German you can be sent to jail. I, fortunately, am an American, so I merely was sent to Paris. Worse things can happen to one.

Source: The State of the World 2010, public lecture in New York City, USA, (July 2010)

Source: Reflections on the Human Condition (1973), p. 127

2005
Context: I think the government should be spying on all Arabs, engaging in torture as a televised spectator sport, dropping daisy cutters wantonly throughout the Middle East and sending liberals to Guantanamo.
But if we must engage in a national debate on half-measures: After 9-11, any president who was not spying on people calling phone numbers associated with terrorists should be impeached for being an inept commander in chief.
With a huge gaping hole in lower Manhattan, I'm not sure why we have to keep reminding people, but we are at war. (Perhaps it's because of the media blackout on images of the 9-11 attack. We're not allowed to see those because seeing planes plowing into the World Trade Center and the Pentagon might make us feel angry and jingoistic.)
Among the things that war entails are: killing people (sometimes innocent), destroying buildings (sometimes innocent) and spying on people (sometimes innocent).
That is why war is a bad thing. But once a war starts, it is going to be finished one way or another, and I have a preference for it coming out one way rather than the other.