Many terrorism watchers warned of attacks in the United States when the war against Iraq began. But it hasn’t happened. (Today, the Department of Homeland Security lowered the color-coded threat level from “orange” to “yellow.”) The most important factor, says the Christian Science Monitor, seems to be the strategy of aggressively pursuing Al Qaeda members. Also important is public vigilance around the world, which may make it tougher for terrorists quietly to carry out complicated planning for large-scale attacks. The fact that the war is relatively brief may be preventing Arab anger from exploding into attacks. “The danger isn’t past, but it has to be diminishing,” says Phil Anderson of the Center for Strategic and International Studies in Washington. Rohan Gunaratna, author of “Inside Al Qaeda,” noted that its operatives in 98 countries have been arrested since 9/11. Public watchfulness, along with myriad homeland-security measures including better airport and port security, is having an impact. “When the public is alert, it’s very hard for terrorists to plan and execute … large-scale attacks,” says Gunaratna.