In practice it strengthens the nation state. It has a purpose, too, for given an innate but not perfect human conservatism, maximising interaction will minimise change. Partly, perhaps, because it would lie outside the concept of the political entirely. Some of liberalism's founding fathers sought to do that as well, but the derivation here is different. It starts from what liberalism does, or seeks to do.
Liberalism aims at maximising interaction.
For some liberals that is a stated goal, with a virtual sacralisation of interaction by Popper and Hayek. Post-war liberal theory, and all market liberalism, refer to processes of interaction, not of withdrawal, evasion, escape or concealment. Current English-language academic practice contrasting it to communitarianism does so on the basis of differing conceptions of the self. However the defence was against the state, not primarily against others. Liberalism more or less requires the individual to submit to interaction, usually with the proviso that rights are not infringed.