For liberals, war is a purely economic calculation whose criteria of justification are decided by whether or not they contravene principles whose evolved historical function is the preservation of capitalist social relations and the imperialist world system (whether the liberal in question is a mystified rube or a demonically englightened ghoul). Similarly, criteria of success or failure in war is based on economic calculation. Look at the U$ yankkkie defences of their proxy war in Ukraine: "no Americans are dying, it will weaken the Russian economy, we must secure our interests". Of course we also know, as evidenced spectacularly by the U$ terrorist bombing of the Nord Stream pipelines, that the key objective is always the preservation of U$ economic hegemony, keeping a competitor economically disadvantaged, taking their economic customers in Europe and forcing them into economic dependence on America LNG.

It's not always that what they know is a lie. Liberals often do know quite a bit, especially the more ghoulish ones. Most of them, yes, are rubes in a lot of respects. But the most basic normative axioms of their thought are detached from reality in a particularly striking way.

Of course when they fail by their own criteria (see: Korea, Vietnam, Afghanistan, Iraq, Yemen, Syria, Libya, etc.....) they are never honest about this and use mental gymnastics to avoid responsibility, because that matters more, because the legitimacy of their views must be defended at all costs. This is inculcated into liberals as a matter of liberal cultural necessity because if it wasn't, they would not be able to adequately defend those same capitalist and imperialist socio-economic systems they rely upon and in terms of which they determine their own self-worth.