The bill allocates $1.2 billion to build 700 miles of security fence along the U.S.-Mexican border. The fence would involve advanced technology sensors and 1,800 towers built by Boeing and equipped with sensors.

Critics of the bill argue that that it will not stop perhaps scores of thousands or hundreds of thousands of people from Mexico from continuing to try and get through every year. They also point out correctly that the bill nowhere tackles the key economic forces driving the immigration. It contains no provisions whatsoever to penalize employers within the United States, especially in the southern and southwestern border-states from employing illegal workers.

As long U.S. federal authorities are prevented from effectively cracking down on such employers, the magnetic pull of better-paying jobs for immigrants will continue to lure them north from Mexico.

However, the significance of the bill should not be casually dismissed either. It is certainly the case that in the long run of decades, generations and centuries, eventually long walls or border fences usually do come tumbling down. But they usually work very well indeed for a very long time first.

The Great Wall of China was famously breached three or four times over the millennia by hoards of barbarian invaders who did conquer China like the 13th century Mongols. But it worked very well for hundreds of years at a time in keeping them out. The German Army, or Wehrmacht, never breached the French Army's Maginot Line in 1940. They had to go around it. In the fall of 1944, the defenses of the Wehrmacht's own Siegfried Line, once it was fully manned, stopped even U.S. Gen. George S. Patton's Third Army in its tracks and helped keep Nazi Germany in the war for another half a year.

In more recent times, the whole world knows that the Berlin Wall came tumbling down in 1989 during the collapse of communism in Central Europe. But it had bought time for the communists and kept East Germany from collapsing for more than 28 years before that finally happened.

Now in the 21st century, passive border defenses are in fashion again thanks to former Israeli Prime Minister Ariel Sharon. During his five stressful years as leader of the Jewish State, Sharon stopped the slaughter of more than 1,100 Israeli civilians, including a large proportion of women and children, by Palestinian suicide bombers by the straightforward expedient of building a massive security barrier, or fence, across the country to keep them out.

The fence continues to work well. Even when Hamas, the Islamic Resistance Movement, lobs over low-tech, very short-range Qassem missiles at Israel over the fence, their cost in casualties so far has been negligible..

Sharon's achievement not only defeated the Second Intifada, it also transformed the strategic assessments of nations and militaries facing guerrilla campaigns based from outside their own borders all around the world

Impressed by the Israeli example, India rapidly followed suit in building a security fence along the Line of Control in Kashmir. Indian security officials later said this fence cut the number of incursions by Islamist guerrillas operating from their havens in Pakistan by as much as 90 percent. The Indians have therefore pushed ahead with building another, even longer fence, around the nation of Bangladesh to cut back on Islamist guerrilla incursions from there.

Even Saudi Arabia has followed the Israeli example by building a massive security fence along its southern border with Yemen. Interestingly, the strategic purpose of the Saudi fence has much more in common with the U.S.-Mexico fence than with the Israeli one. The Israeli fence was built to choke off a vicious suicide bomber offensive against civilians. The Saudi fence, like the U.S. one, was built primarily to keep out a flood of illegal immigrants from a far poorer neighboring country to the south, and to prevent terrorist groups like al-Qaida from being able to funnel agents and weapons at will across the frontier.

In the long term, the success of the border fence will be determined by grand strategic developments on both sides of the Rio Grande. Continued stability and improved economic growth in Mexico will be the most important factor in cutting back illegal immigration pressures. And on the northern side, even if the current Bush administration and its deeply divided Republican Party will not crack down on the almost universal employment of illegal immigrants, state governments and future administrations may.

Either way, the current legislation does not appear to be designed to solve current problems so much as to alleviate them. It appears to be a measure designed to buy time. But time is often the most precious commodity any political measure can buy.

Related Links
News and analysis about the Global War Against Terror at SpaceWar.com