I am not being smug, just genuinely curious - can you provide contemporary examples of a major nation without border security?

Major nations, in the modern era of national and supra-national states, tend to either have their own state or dominate a supranational state, and so tend to have border security (which is necessary for an effective state, though less important to a nation.)

Of course, several centuries in to the era of the nation-state as a dominant form, lots of people confuse states and nations.