“"War is the continuation of politics." In this sense war is politics and war itself is a political action; since ancient times there has never been a war that did not have a political character.”

2000s, Where the Right Went Wrong (2004)

On Protracted Warfare (1938)
Variant: Politics is war without bloodshed, while war is politics with bloodshed.
Context: "War is the continuation of politics." In this sense war is politics and war itself is a political action; since ancient times there has never been a war that did not have a political character... But war has its own particular characteristics and in this sense it cannot be equated with politics in general. "War is the continuation of politics by other means."When politics develops to a certain stage beyond which it cannot proceed by usual means, ware breaks out to sweep the obstacles from the way. When the obstacle is removed and our political aim attained the war will stop. But if the obstacle is not completely swept away, the war will have to continue till the aim is fully accomplished.... It can therefore be said the politics is war without bloodshed while war is politics with bloodshed.

Variant: War Is Merely the Continuation of Policy by Other Means
Source: On War (1832), Book 1, Chapter 1, Section 24, in the Princeton University Press translation (1976)
Variant translation: War is merely the continuation of politics by other means.
Context: War Is Merely the Continuation of Policy by Other Means
We see, therefore, that war is not merely an act of policy but a true political instrument, a continuation of political intercourse carried on with other means. What remains peculiar to war is simply the peculiar nature of its means.

Speech at the Coliseum in St. Louis, Missouri, on the Peace Treaty and the League of Nations (5 September 1919), as published in "The Public Papers of Woodrow Wilson (Authorized Edition) War and Peace: Presidential Messages, Addresses, and Public Papers (1917-1924) by Woodrow Wilson Volume I Page 638. Addresses Delivered by President Wilson on his Western Tour - September 4 To September 25, 1919. From 66th Congress, 1st Session, Senate Document No. 120
1910s

From a conversational exchange with Harold Begbie, as cited in Master Workers, Begbie, Methuen & Co. (1906), p. 177.
Early career years (1898–1929)

Source: A Soldier's Story (1951), p. xi.

World War T http://takimag.com/article/world_war_t_steve_sailer/print#axzz4A3cQmle0, Taki's Magazine, January 22, 2014

Source: Power Kills: Democracy as a Method of Nonviolence(1997), p. 114

During an after-dinner discussion in Munich https://books.google.com/books?id=2zxfyeUHKEAC&pg=PA69 (1933), regarding the American Civil War
Disputed, The Testament of Adolf Hitler (1945)
Context: This is the last disgusting death-rattle of a corrupt and outworn system which is a blot on the history of this people. Since the civil war, in which the southern states were conquered, against all historical logic and sound sense, the American people have been in a condition of political and popular decay. In that war, it was not the Southern States, but the American people themselves who were conquered. In this spurious blossoming of economic progress and power politics, America has ever since been drawn deeper into the mire of progressive self-destruction. The beginnings of a great new social order based on the principle of slavery and inequality were destroyed by that war, and with them also the embryo of a future truly great America that would not have been ruled by a corrupt caste of tradesmen, but by a real Herren-class that would have swept away all the falsities of liberty and equality.