by Zack Beauchamp
David Bosco pinpoints "a fundamental difference between the neoconservative worldview and the liberal interventionist one:"
[It is] the role of international institutions and law. Those of a neoconservative persuasion aren't much interested in global architecture; they're intent on achieving liberal, democratic governance at the national level whenever and wherever possible. Indeed, they believe that consensus-based international organizations and procedures tend to obstruct that enterprise as often as facilitate it. Liberal interventionists share the desire to spread freedom and the conviction that outsiders can help do so, but they also care deeply about building international architecture (almost always) and respecting international rules (usually).
This is the most commonly cited difference between the two intellectual camps, but I'd add another: attitudes towards war. While both liberals and neoconservatives are often supportive of military interventions, the former group doesn't require a belief in the general efficacy of military force as a condition of entry.
Liberals often differ sharply about, for example, humanitarian intervention: it's entirely coherent to self-describe as both a foreign policy liberal and believe that humanitarian intervention usually does more harm than good. Neoconservatism, by contrast, makes a belief in the morality and efficacy of preventative wars against rogue states (Iraq, Iran), nation-building endeavors (Afghanistan post-2009), and overwhelming US military dominance more broadly into bedrock principles. While liberals might endorse any or all of those three, it's not at all requried by liberal commitments that they do so.
In other words, liberalism simpliciter leaves the utility of force as an open, contextual question, while neoconservatism makes belief in it central to its vision of American foreign policy.