I agree with you on parts of that, the old "Si vis Pacem, Para Bellum" still stands, and the people who speaks about reducing the armed forces on the grounds that "It's so peacefull now" and "It could never happen again" has obvilously spendt their history lessons sleeping on the last row.
But the idea on anyone invading the USA is still too far fetched.
An amphibious landing on US beaches is peanuts, assuming you have the strength and manpower to do so and tolerate losses, those beaches are simply impossible to defend.
And that fact wouldn't change even if you lined up every shotgun owning redneck you can manage to sniff up.
The coastline is simply too long to hold, and so are the vast landscape behind it.
But the vast landscape behind it also make it impossible to invade, at least if the invader seeks to actually gain something.
The frontline would be to wide, the forces to spread out, and the supply lines too long.
Very much the same factors that has saved Russia/Soviet Union for centuries.
There's alway a next line of defence behind the one the defenders are leaving, and there's no relief for the invaders who are short of supplies and in constant fear of being outflanked.
And for the Japs, they didn't have the manpower, even if they were crazy enough to attempt anything like it.
Only brutal force and total disregard for humanity as such left them in control of southeast Asia for the time they were.
But you better prepare for an invation of USA, if nothing else, it makes you sleep better.
