Israel and Sri Lanka face suicide bombers operating from nearby sanctuaries. Suicide bombers attacking in the United States don't have those, which makes such attacks prohibitively expensive for their supporting organizations. They therefore prefer to attack higher value targets, notably airliners, of which the most recent example was the shoebomber named Reid.
The Palestinian suicide bomber apparatus revealed in captured documents shows there will be significant problems getting the bombers themselves into the US without leaving a quite traceable trail. Palestinian and most Tamil suicide bombers aren't trained, sophisticated terrorists capable of blending in the population of a foreign country. They have a short range in space and time - Palestinians attack the same day they cross into Israel. Tamil suicide bombers generally attack political victims as opposed to conducting general terror attacks against ordinary civilians as Palestinian terrorists do to Israelis.
Foreign terrorists have two choices in conducting multiple suicide bomber attacks in America similar to those conducted against Israel. One is to use their scarce trained, sophisticated, personnel as the suicide bombers (which is why there are been so few Tamil suicide attacks outside Ceylon, all on high value targets), which means termination of the bombing campaign when those all die (most of the 9/11 hijackers didn't know they were on suicide missions). The second option is to risk those same personnel here or in Canada/Mexico in support roles, for less trained bombers, with detectable signatures which our security and drug enforcement agencies will pick up fairly fast with the same result - termination of the bombing campaign through loss of their important personnel.
The critical difference between the vulnerability of Israel and Sri Lanka to suicide bombers, and America's vulnerability, is that the terrorists have sanctuaries in areas with direct land access to the former. Sri Lanka lacks the military capability to eliminate the Tamil sanctuaries in northern Ceylon. Israel has until recently lacked the political will to attack Palestinian terrorist sanctuaries in the West Bank and Gaza.
Canada and Mexico have not permitted such sanctuaries for foreign terrorists. They are slack in letting suspicious foreigners into their countries, but so is the United States. If we get serious, Canada might also, though Mexico lacks the means to do so due to social problems and corruption.
The United States might suffer sporadic, as opposed to extended, suicide bomber attacks against ordinary civilians, but those will not at all compare in numbers to what the Palestinians did to Israel before the latter finally developed the nerve to attack terrorist bases in the West Bank. The absence of suicide bomber attacks in the US since 9/11, even against high value or vulnerable political targets, indicates lack of terrorist capability to conduct them, most likely for the geographic reasons mentioned.
The possibility of an extended suicide bombing campaign in Europe is much less than reputed for the same reason, though not as low as in the US due to the greater numbers of unassimilated Arab immigrants in Europe providing more cover for terrorists to operate in. Such cover is not a substitute for a geographic sanctuary, however.
Israel's vulnerability to suicide bomber attack against civilians is more the exception than the rule. -- Thomas M. Holsinger
Geography Protects America From Suicide Bombers- The United States need not fear an extended suicide bombing campaign similar to those afflicting Israel and Sri Lanka (Ceylon) due to geographic factors.