1) Toppling of the Taliban. Getting rid of the government of Afghanistan and installing troops has hit the enemy at one of its largest bases of operation.
2) War in Iraq. This is draining men; weapons and money like a dark hole. It is very expensive to wage war for both sides, and the U.S. has far more resources to work with. Not to mention the poor match-up for them, attacking the best equipped army in the world in the worst battlefield environment that they could ask for.
3) Allowing greater transparency between agencies of the U.S. government. Allowing them to talk to each other has foiled several potential attacks. Possibly ‘home grown’, but the ideology is very similar to that of our enemy.
4) Greater cooperation between allied nation-states. I am referring to our ability to launch both ground and air attacks within Pakistan. The ground attack portion has been stopped fairly early in the process. (2003) However, the air attacks are still being made, 6 and ½ years later. We have also launched air attacks into other countries notably, inside Yemen, with good results.
5) The Israeli war against Hezbollah. That 30-day war killed an estimated 2000 and burned up a lot of resources that had to be replaced. This can easily be expanded into the overall effect that Israel has upon terrorism in general. Our enemies hate them as well as us. To kill or eliminate any of the resources that are targeted upon Israel is as good for Israel as it is for us.
Many people will disagree with numbers 2 and 5.
Referring to number 2, I believe that the war in Iraq has placed the enemy on the strategic defensive. The enemy must react to our presence in Iraq. They MUST attack our army. The mismatch is good for us. And most importantly, the war is forcing all of those ‘new’ terrorists into the open. This is vital, as one of the greatest problems in fighting terrorism is identifying who they are and who supports them.
Referring to number 5, I believe this to be the case because this is an ideological war. Israel and the U.S. have ideologies that have far more in common than the ideology of our enemy. Our open societies are one of the ideas that are hated by our enemy, above most others. One key indicator is the repeated suicide attack. Only one prior occurrence of this has happened in all of recorded history. As demonstrated in both cases, ideological persuasion is necessary to overcome this most basic instinct. This is the common denominator.