You're changing the subject, though. The state having the monopoly on violence is a trait of civil societies in general. You can break a liberal democracy in many, many ways entirely unrelated to that issue, which is ultimately just that individual citizens aren't allowed to enact their will through violent acts and instead must appeal to the state for restitution when they are wronged.
The US's issues aren't that the government doesn't allow its private citizens to legally act violently (the exact opposite is a problem in the US, in fact), and having a monopoly on violence doesn't bear one way or the other on whether a country's international policy is compliant with international law.