“Nobody is ever involved in an aggressive war; it's always a defensive war -- on both sides.”

Gary Brecher at exile.ru/authors, 2002

As quoted by Cicero in De Officiis, Book I, Chapter XII

Source: Friday (1982), Chapter 4 (p. 37)

The King's Twenty-Five Years. III. The Coronation and the Agadir Crisis. The Evening Standard, 4 May 1935
Reproduced in The Collected Essays of Sir Winston Churchill, Vol III, Churchill and People, Centenary Edition (1976), Library of Imperial History, p. 351-2. ISBN 0903988445
The 1930s

Source: Imperialism, The Highest Stage of Capitalism (1917)

Your Inner Awakening

Peace and the Public Mind (1935)
Context: Now, please don't misunderstand me. When I point out that all our wars for a thousand years have been fought in other people's countries, I do not mean that any of these wars was necessarily aggressive. They may well have been, everyone of them, defensive. But plainly they were not defensive of soil, territory. Of what then were they defensive? They were defensive of the nation's interests, rights; interests which may well collide with the interests of other nations in any part of the world... Nations do so differ as to what their respective rights are and differ sincerely. And often the question, which of the two is right, is extremely difficult, as anyone who has attempted to disentangle rival territorial claims in the Balkans or elsewhere knows only too well.

As quoted in an interview in Reason magazine (February 1973) http://www.antiwar.com/orig/rothbard_on_war.html.
Context: All interstate wars intensify aggression – maximize it … some wars are even more unjust than others. In other words, all government wars are unjust, although some governments have less unjust claims…

2000s, The Real Abraham Lincoln: A Debate (2002), Q&A