> The Internet was specifically designed to be maximally decentralized to be robust even to war.

This is a bit naive. Until TLS, TCP traffic on down was sent in the clear. Most traffic used to be sent in the clear. This is what makes packet filtering and DPI possible. Moreover things like DNS Zones and IP address assignment are very centralized. There are cool projects out there that aim to be more decentralized internets, but unfortunately the original Internet was just not very good at being robust.

It was robust against disruption, but it was not secure against attacks.

The threat model that was considered was bombs blowing up routers, but at the time, intermediaries intercepting traffic was not considered.