it seems kind of moot to point this out, but the purpose of terrorism it to. . . scare your enemy. Now to be clear the modern form of terrorism is entirely directed at civilians, because actually fighting in a military engagement between the Man-dress Malitia and a real honest to God Army is something rather akin to suicide. There certainly many many men that signed up for that form of suicide, whether the promise of 72 virgins, they were bored, or they were actually deluded enough to think they could win doesn't really matter, most of those men are dead or unable to fight anymore. On some level, however Terrorism does actually work. Not in the way that they obviously hopped, because let's face it we didn't capitulate, but it has forced us to alter the way we do business in this country.
When it comes to our military, we tend to shy away from actually instilling fear in the civilian population. In fact we try to do the exact opposite, we try, very hard I might add, to make them love us. We can terrify them, and at a moments notice turn around and hand out soccer balls. It is actually quite confusing both to friend and foe alike. So lets be clear, that instilling fear in enemies or even potential enemies or even the people that don't quite get along with you is actually a very good thing when it comes to foreign relations.
I'll start with purely military matters, and I'll draw only from American history, because that will be the most easily understandable. So where do you have Armies inflicting terror upon each other? Well I will naturally enough point to the Civil War, and the high point of the Confederacy in early 1863. After the absolute disaster of Fredricksburg, the new Union commander Joseph Hooker (side note where the term "Hookers" comes from) sought to break the stalemate at Fredricksburg, and sought to slip around Lee, and catch him by suprise. Using his vast army, he kept a force in place to threaten Fredricksburg, then moved North and East. Only problem is Lee knew what he was doing so he divided his force (against all military logic of the time) and followed hooker. Once the battle lines were drawn at Chancellorsville, Lee again divided his forces, sending Lt General Jackson on a 19 mile march around the Union lines, through the woods.
Jackson attacked 2 hours before dark, to minimize the damage should the battle go against him, into union forces that were completely unprepared for him. When encamped troops looked up to see 28,000 Confederates charging toward them, not making the trademark rebel yell until they were right on top of them. To call the response a route would be kind. many regiments broke and ran in terror, leaving their weapons, ammo and supplies behind. Hooker himself was thrown into confusion, and started giving orders that made no sense further compounding the mistakes already made. In this way Lee was able to make his much smaller force(s) and squarely defeat a much larger army.
It can be applied to even more battles, some even more recently. There are a few notable examples, like Patton's 3rd Army in the latter part of the European Theater, and even the Inchon landing and 2nd Battle for Seoul, trapped a large amount of DPRK troops and almost caused a complete capitulation of the North Koreans, indeed if not for the intervention of China, Korea would be unified under a true democratic government. However where America has truly inspired terror in an adversary could well be in Iraq, during Desert Storm. The "hook" maneuver both trapped the Iraqi army in Kuwait, and also happened so fast that the enemy didn't have time to react. The result was a route that the Us exploited to great effect causing the 19th largest army in the world to become so much slag. They had not even begun to recover 12 years later when the US invaded and finished the job.
And therein lies a lesson we can take for foreign relations, and international politics. The entire world was so sure that we would not "go it alone" and that we would not invade Iraq (regardless of the "legality"). The world was sure that Vietnam had soured America in this kind of warfare. That we actually went ahead and did it. It shocked a lot of people. One of the people it shocked was Qaddafi, who was already twitchy after we nearly killed him following Operation Eldorado Canyon, but OIF convinced him that Libya would be next should he not straiten up. Even Iran began to sing a different tune (for a time). Where we went wrong, actually has nothing to do with the political reasons to invade, but not to have enough troops to maintain security once the invasion was complete. Iraq, unlike Afghanistan, has not only a history and cultural identity but a functioning if not first world at least second or upper tier third world infrastructure. Indeed had we been able to maintain the Iraqi Army, and had enough troops to lock the country down for say 6 months, we might have easily been able to shave 3 or 4 years off the occupation, and we might well not have had to deal with the near civil war that we saw in 2006-2007.
From the mid 70's till the early 80's a majority of the world was "secure" in the knowledge that we wouldn't act preemptively, that we couldn't. Rather than challenge the USSR we sought Detente. Rather than bolster tenious governments we cut our losses. Indeed it wasn't really until Desert Storm that people thought that America would do more than drop a few bombs to send a message. OEF and OIF have shown that the US can and will sustain a long drawn out conflict. We should not be so loath to embrace the mantra of the guys that bully the bullies. We may wish to "use our words" but sadly there are far too many countries (and insurgent groups) that simply will not respect that. Even the First World bastion of Europe is starting to suffer tremendously because it will not take clear and definitive action, even on simple issues that do not require military action.
My Dad's old boat, the USS Barb had a slogan: Cavaet Tyrannis. Tyrants Beware. It is doubtful that the world will stabilize, in a way we would hope. Economic upheaval almost always gives rise to tyranny. We should be ready for being called upon again to depose tyrants. It is perhaps a good thing then that we seek to instill as much fear in such men as we possibly can. By instilling fear in men who rule by fear we might actually avoid unnecessary confrontations or even cause reforms. We will have to remember, however that our principles must always guide us, that our credibility must be maintained, even as we tare down more stature of dictators.