The author mentions how "western" powers controlled a much greater portion of the worlds population in 1900.
Assuming territorial instincts are threatened by losing this control(India, Pakistan, Bangladesh, Indochina, most of Africa, the Middle East), the author seems to be implying a preferrable arrangement would be that western powers still controlled these areas.
If these territories were controlled by western powers, as colonies or commonwealths or whatever, the citizens there would inevitably acquire some type of citizenship status in the ruling nation. Most American Colonists considered themselves British citizens until a few years into the Revolutionary War. There are 3,994,259 Puerto Ricans in Puerto Rico and 3,800,000 Puerto Ricans in the 50 United States.
Europe couldn't handle 500 million additional Indians, 200 million additional Africans, and a few hundred million people from the various Southeast Asian countries.
The sporadic terrorist excursions of Saudi Arabians are an inevitable part of massive population density growth and modern boredom. In America our education system isn't very efficient, but even most poor people are pretty wealthy, so this portion of the population can exert itself in conventional crime. Thats why 2 or 3 million americans are in jail or prison.
It is best to not feel threatened by Islam or Asia. These places are very close to catastrophe, because they are so overpopulated. Any threat they possess is a very temporary economic stature brought about by our own leaders taking free trade way too far. India and China and the Middle East will probably collapse in some kind of ethnic or demographic war-riots once a few lean crop years hit or too many sectors of the old economy are obsoleted at once.
http://en.wikipedia.org/wiki/List_of_wa ... death_toll
As you can see, every few hundred years a few ten or twenty percent of China's population is killed in a civil war or Mongol invasion. China has 800 million more people than it had 60 years ago, and has gone through greater structural change than at any time in its history. There will be a lot of people wondering why they can't have the stuff on TV at the same time economics forces down the value of labor and prostitution, and drives up the cost of living.
As you can also see from the above post, Europe was wracked with some pretty severe internal wars over distinctions we think are fairly ridiculous today, but the leaders of each side thought the other was a severe threat.
http://en.wikipedia.org/wiki/Wilmington_Race_Riot
Here is another story of violent threats erupting into the overthrow of government and freedom. A single white civil war veteran orchestrated the overthrow of a government of a reasonably integrated and prosperous southern town.
http://en.wikipedia.org/wiki/Ave_Maria%2C_Florida
In the future, Americans will mostly be threatened by other Americans. They'll be fighting over what their kids should be watching on cable television. it could get violent. The Founder of the Dominoes pizza chain is building an entire city just for people who watch a particular set of programs on cable television and prefer their discount drug stores to not carry contraceptives.
The West isn't threated by any Non-West Parties. Most of the Middle East is Doomed. Most of China and India is Doomed. Maybe a billion people will survive in all of Asia. The rest will be obsoleted by economics. I mean, they probably aren't going to live in outer space or on Mars. it is very sad.