A good example of how political philosophy is driven by ethics.
Here is Engels, Karl Marx’s collaborator in writing The Communist Manifesto and other works, criticizing liberals despite nineteenth-century liberalism’s great accomplishment in reducing war and promoting peace between nations:
“You have brought about the fraternization of the peoples — but the fraternity is the fraternity of thieves. You have reduced the number of wars — to earn all the bigger profits in peace, to intensify to the utmost the enmity between individuals, the ignominious war of competition! When have you done anything ‘out of pure humanity,’ from consciousness of the futility of the opposition between the general and the individual interest? When have you been moral without being interested, without harboring at the back of your mind immoral, egoistical motives?” 
1. In the second sentence Engels subscribes to the “capitalist peace” thesis — i.e., that free market trade promotes peace between nations: one doesn’t want to harm one’s customers or one’s suppliers with whom one has profitable relations. Interesting, since typically (or when it suits their purposes) leftists and especially Marxists argue that capitalism causes war by promoting competition for economic gain. But while Engels grants that the capitalist peace thesis is true, he doesn’t like it.
2. Engels is an anti-egoist and anti-consequentialist: the consequences of liberalism — peace, fraternity, and mutually-beneficial transactions — count for nothing because they come from “egoistical motives.”
3. And Engels’s account of proper motivation is Kantian. The final sentence requiring that one be “moral without being interested” is straight out of Immanuel Kant’s Groundwork: “Now an action done from duty must wholly exclude the influence of inclination,” and “I am willing to allow that most of our actions many accord with duty; but if we look more closely at our scheming and striving, we everywhere come across the dear self, which is always turning up; and it is on this that the purpose of our actions is based — not on the strict command of duty, which would often require self-denial.” 
 Friedrich Engels, “Outlines of a Critique of Political Economy.” Quoted in Tom Palmer, editor, After the Welfare State, Jameson Books/Students for Liberty/Atlas Network, 2012, p. 37. [Thanks to Richard Lorenc for bringing the quotation to my attention.]
 Immanuel Kant, Groundwork of the Metaphysics of Morals, translated by H. J. Paton, Harper Torchbooks, Sections 397 and 407.
Is commerce rendering war obsolete?