Admission to the system as sovereign is now codified and institutionalized by the United Nations. In principle, this includes acceptance of universal human rights. Wagar may scoff at how powerless is the UN to enforce any such standard. Yet one might have said the same 200 years ago about slavery, or 100 years ago about colonialism, or even 50 years ago about racist segregation. The definition of a legitimate state now includes them all, as even a state as powerful as South Africa was forced to finally admit.
National cultures are highly diverse, often inconsistent, and constantly evolving.
They change in response to global capitalist and other processes without any necessary loss of identity. People can hold allegiance to both national and global principles, just as we maintain loyalty to both family and nation. Admittedly powerless itself, the UN increasingly serves as the medium through which the rules of interstate relations are elaborated and enforced. States support UN and other interstate governance of the interstate system not out of moral exhortation, but out of material self-interest. The greater the number of states and the more integrated their economies, the greater the importance of a supra-state governance of interstate relations.