Other countries do have problems, John, offhand we in the UK blame you guys (mildly, we know we have transgressed too, a lot) for grey squirrels and for signal crayfish. We are also permanently on the watch for Colorado beetle, which is one we definitely don't want.

We also blame your neighbours for Canada Geese, and coypu but there are plenty of other sources of nuisance species, witness Himalayan balsam, muntjac deer, Russian vine, Japanese knotweed, and rabbits of course.

The root of the problem is that humans have a history of both invading and being invaded, interspersed with global travel, and in all this travel other species go along with the humans whether by accident or by design. Nations can try to raise barriers but I suspect that as a rule they are merely delaying what is inevitable, and that nature wins every time in the end.