The problem with only waging war when someone attacks your country or its citizens is that you've then become completely predictable. If the United States did this, then it would be rendered irrelevant by such a policy. All an enemy nation would have to do is attack and swallow up neighboring countries, robbing them of their resources and as long as Americans didn't get killed, they'd be allowed to simply proceed. Of course eventually they'd be big enough to take on the U.S. militarily.
If the US had adapted such a policy in WWII, we wouldn't have entered the European theater. Germany would have won in Europe. In 1942, by the time that the US declared war against Germany and Italy, the only European nation that didn't have German troops in it was Britian (Spain had German "advisors" from their recent revolution, and yeah, Switzerland didn't have any German troops but they also couldn't resist any serious German offensive). Germany could have easily fought a holding action against Britian and turned its resources against the Soviet Union and it likely would have won. That would be quite a different world.
We have alliances in the world and those alliances say that we will provide aid, including (especially) military aid, to those allies if they need it. Those alliances have value to the United States and to the world. Nations don't often attack U.S. allies because they know that the U.S. will take action. The allies themselves rely on that protection, and frankly, if Israel thought that we wouldn't be there when they needed us, I think they'd likely consider using their nuclear weapons to defend themselves.
Perhaps you mght think that we can simply extend the policy, we only go to war when our citizens or allies are attacked. If we took such a stance, then we still have the problem of non-allied nations going to war with each other. let's say that a dictator in Africa decided to take over the continent. With a bit of planning he could probably roll over neighboring countries and could do so as long as he didn't attack a US ally. Of course if he controlled enough of Africa, he'd have enough resources to perhaps not worry about attacking a U.S. ally. Even if he didn't get that big, the war that he waged would disrupt world economies (including ours), and would kill possibly millions of lives (dictators and tyrants always kill huge numbers of civilians in the lands they've conquered).
Add to that, the new threat in the world. The biggest threat to the U.S. isn't another nation. The biggest threat is a destabilizing force such as terrorism. A small number of terrorist can inflict damage well out of proportion to their size. One man can poison a whole city. One man can blow up a building killing hundreds. The fact that these people are willing to die to achieve their ends means that it becomes very hard to stop them, especially since we choose (justifiably) to restrict the means that we use to stop them.
You say give them aid, but if aid is given to the governments that are injuring their people, then those people never get help and the government has more resources to hurt them. The U.S. government, and any other government, cannot give aid directly to citizens of another country, thus giving aid isn't really an option. Besides, what aid would you propose giving when a tyrant is running a genocide program? What aid do you think will stop genital mutilation? What aid do you see as the solution to slavery?

If you're waiting for the UN to take care of worldwide atrocities, then you'll be waiting a long, long time. The UN has shown repeatedly that it lacks the resolve to actually do anything beyond passing resolutions. It won't take a firm stance against anyone because that might lead to war and the UN isn't interested in war. Part of the reason is that war tends to unveil graft (see the oil for food scandal) and corruption. Part of the reason is that a large percentage of the UN members are dictatorships that will vote against any resolution against another dictator for fear that they will be next. Part of the reason is that members of the security council are not unified as to what is important in the world, and while they debate, people die. Personally, I'd rather be part of a movement that helped these people live.

Finally, don't think that defeating Saddam Hussein created terrorists. Terrorists have existed under different names for centuries. Anyone who intentionally attacks a civilian is a terrorist, and killing civilians has been going on for the recorded history of the world. You're right, we cannot see them on the street, but they leave a trail and that trail is being followed by the US and its allies. At least by openly declaring the war against them, it raises the alert level of civilians so that we can pay attention and have some hope of protecting our families from these people.


Shane,

Do you have evidence that the US has stolen oil from Iraq, or do you simply accept the propaganda that says that sooner or later we'll do it?

-- Jeff

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"Government is not the solution to our problem, government is the problem." --Ronald Reagan