And amid the skyscrapers of New York, where war came home one clear September day, helmeted tactical officers stood guard on Wall Street as a new war unfolded in the sand dunes and streets of Iraq.
The nation battened down under security not seen since the Sept. 11 attacks as U.S. forces attacked on Wednesday night.
The State Department Wednesday evening issued an updated worldwide caution, reports CBS News Correspondent Charles Wolfson, warning U.S. citizens abroad of the potential for anti-American violence. The threats include the possibility of attacks by terrorist groups, and notes that terrorists do not distinguish between official and civilian targets.
A separate warning was issued to caution all Americans in the Middle East and North Africa.
School officials in Washington's Maryland suburbs canceled field trips not only to the Nation's Capital, but also other East Coast cities.
Authorities in the U.S. fanned out to power plants, bridges, state capitols and other facilities to shield them against possible retaliatory strikes.
Though most protections had been in place since the terror alert status was raised from "elevated" to "high" Monday night, some states planned to further tighten security now that war has begun.
"The first 96 hours of the war is very important, and it deserves special consideration," said Missouri's homeland security adviser, Tim Daniel, who planned to ask Gov. Bob Holden on Thursday to restrict access at the Capitol to make it more difficult for unscheduled tour groups to visit the building.
Kansas Gov. Kathleen Sebelius also planned to heighten security Thursday at the Capitol complex in Topeka. She ordered state employees to wear their identification cards and said visitors to the Statehouse and state office buildings would be required to sign in.
The Kansas Bureau of Investigation was ordered to review the files of people suspected of having ties or contact with terrorist organizations.
"We're taking this seriously," Sebelius said after a conference call Wednesday night in which White House staff and homeland security aides briefed governors on the airstrikes.
The countermeasures were most conspicuous in the two cities terrorists targeted on Sept. 11.
In Washington, the White House was closed to tourists as police used the city's network of 14 closed circuit cameras to monitor activity at landmarks, including the Washington Monument, the Capitol and Union Station.
In New York, police prowled city streets with bomb-sniffing dogs, submachine guns and radiation detectors. Officials worried about suicide bombers and armed takeovers of television stations.
"There is a two-front war here," Mayor Michael Bloomberg said. "One is on the streets of our cities, and one is overseas."
In Iowa, officials arrived at the state's Emergency Operations Center late Wednesday to monitor the first hours of the war and prepare any necessary response. Since Monday, guards have kept a 24-hour watch at the Union Pacific and Burlington Northern Santa Fe rail bridges over the Mississippi River.
Authorities at the North American Aerospace Defense Command and the new Northern Command in Colorado Springs said war could mean more jet fighters patrolling the skies around big cities and ground-based air defenses around population centers.
Airports, schools, truck stops, casinos — all saw increased security in the days leading up to war.
At Atlanta's Hartsfield International Airport, one of the world's busiest, orange barricades outside parking lots kept cars at least 300 feet from the terminal. In Virginia, Fairfax County public schools canceled all field trips to Washington and New York.
In Berkshire, Ohio, truck driver Dave Worden said he didn't mind the increased inspections at highway weigh stations.
"I'm willing to do what it takes for the country to be protected," Worden said.