[Antoninus]

At some moment Romans stopped to have children and they got replaced by the barbarians.

It was quite early in the game, actually. Augustus Caesar actually had to pass a law against bachelorhood to encourage the lay-about Roman men to marry and have children. The Romans existed on the stored up capital of their military system and societal prestige for a good 500 years after that, but their society was rotting from within for much of that time. When the Goths broke through in 378, the Empire was more or less an empty shell.

Thus Western civilization at present. Any guesses as to where the big barbarian break-through will happen this time?

[fire_eye]

It was quite early in the game, actually. Augustus Caesar actually had to pass a law against bachelorhood to encourage the lay-about Roman men to marry and have children.

That's the fact of the matter... Given the combination of education and wealth, people just stop having children - which is exactly the opposite of what's good for civilization. The wealthy and well-educated are exactly who should be having large families, while those who are too stupid or too poor to raise children, shouldn't be breeding at all.

But do we want to turn the power to regulate such things loose in the hands of a Government?

Regardless, for all our supposed intelligence we sit and watch as history repeats itself...

Any guesses as to where the big barbarian break-through will happen this time?

"Where" is the wrong question in the age of global transportation. The only question is "by whom". The entire panoply of third-world rodentiae has got its eye on us...