National sovereignty unimportant if government acts properly
Governments have only one legitimate function and that is to protect individual liberty. And if governments restricted their activities to this role no one would care about national sovereignty. If you owned a piece of property why would you care which government protected your property rights? Would there be a dispute if the country next to you said they wanted to protect your property rights? If you entered into a contract would you care who assisted you in enforcing the contract? Similarly, would you care which government protected you against theft or protected your life. No
The only time that citizens care about which government is exercising its authority is when those governments are exceeding their proper role and exercising authority that they should not have, such as to steal from you (even if it is via the ballot box and even if they sanitize the theft by calling it taxation), or regulating your peaceful activities, or forcibly redistributing your wealth. When government engages in these activities we all must be concerned and involved and fight to make sure that government doesn’t steal too much from us and that, if it does, we get a large portion of the stolen property back in form of payments and benefits.
Unfortunately, we live in a world where the majority of what government does falls into the second category, stealing our money, regulating our behavior, and redistributing our wealth. Imagine a world where governments only performed their proper role; nothing to kill or die for. It’s easy if you try.