Five years ago, on March 20, 2003, U.S.-led forces invaded Iraq to overthrow a dictatorship that President Bush accused of developing weapons of mass destruction. No WMD were ever found. As VOA's Bill Rodgers reports in this first in a series of reports on the Iraq war, the fight against an insurgency continues even though a troop surge last year has helped reduce the level of violence.

Combat in Iraq, and U.S. troops are still battling insurgents, five years after the invasion.

A U.S.-led coalition of some 300,000 troops launched the attack on Iraq in the pre-dawn hours of March 20, 2003. The objective was to topple Saddam Hussein's dictatorship - accused by the United States and its coalition partners of possessing and actively developing weapons of mass destruction.

In the build-up to the war, then U.S. Secretary of State Colin Powell laid out the case against Iraq before the U.N. Security Council. In his presentation, he displayed aerial photographs of alleged chemical weapons sites and mobile labs designed to make nerve agents.

"Ladies and gentlemen, these are sophisticated facilities. For example, they can produce anthrax and botulinum toxin - in fact they can produce enough dry biological agent to kill thousands upon thousands of people," he said.

U.S.-led forces soon achieved the invasion's main objective - overthrowing Saddam Hussein's regime. Saddam himself was captured in December 2003, and then executed three years later after a lengthy trial.

But no weapons of mass destruction were ever found, despite thorough searches of the Iraqi countryside by U.S. soldiers and teams of weapons specialists. By 2004, it was clear that any WMD Saddam Hussein possessed had been destroyed in the 1990s.

Meanwhile, an insurgency initially made up mainly of Sunni fighters grew in strength, taking a heavy toll on U.S. forces through roadside bombs and other attacks. Iraqi civilians, especially Shi'ites, also were targeted and many were killed.

Anthony Cordesman, a military expert at the Center for Strategic and International Studies, says the Bush administration was unprepared to deal with the invasion's aftermath.

"We went into Iraq prepared for one kind of war which was to overthrow Saddam's regime and defeat Iraq's conventional forces. We had the illusion we wouldn't need stability operations and nation-building," he said. "We were unprepared for what happened, we did not create the conditions for stability."

Despite free elections and the formation of a representative government, instability grew.

Civilian casualties mounted, from car bombs and other attacks carried out by Sunni and Shi'ite militias. Al-Qaida in Iraq was behind many of the bombings in a drive to escalate sectarian violence. By 2006, the country bordered on civil war.

In early 2007, President Bush ordered an additional 30,000 troops to Iraq in an effort to quell the violence. The troop surge, and new tactics of holding areas after insurgents were expelled, brought a measure of calm to parts of Baghdad and other areas of Iraq. Civilian deaths are down 70 percent from a year ago. In once violent Anbar province, the U.S. military says there are fewer than 20 incidents a week - compared to over 300 in October 2006.

One reason for the decline in attacks is that many former Sunni fighters have turned against al-Qaida and are helping U.S. forces maintain security.

"We capitalized on a spontaneous tribal uprising against al-Qaida. That allowed us to create the "Sons of Iraq", a force that now has some 90,000 men about three times the size of our surge," added Anthony Cordesman.  "Al-Qaida helped us immeasurably. I think we have to give credit to our enemy. They did so much damage to themselves in alienating tribal groups and Sunnis, in driving former insurgents to work with U.S. troops, that oddly enough one of our strongest allies in making this work was our enemy."

The top commander in Iraq, General David Petraeus developed the surge strategy, but expressed caution about its success while speaking recently with VOA's Persian News Network.

"We can certainly say the security aspect of the surge has achieved considerable progress. I wouldn't ever use the word success or victory or anything like that."

He later told the Washington Post newspaper that the Iraqi government has made insufficient progress in achieving national reconciliation and providing basic public services. One of the main objectives of the surge was to reduce the level of violence so that the Shi'ite-dominated government could take advantage of the lull to move forward on these. General Petraeus told VOA much more needs to be done.

"Nothing is easy here, progress is difficult to achieve and it is difficult to sustain and build on. There has been progress, we're intending to try to build on it, to try to cement some of the gains, because so far they are tenuous and fragile. They require national political acts of reconciliation, resolving the national political issues."

The Iraq war is now the second-longest in modern U.S. history, with almost 4,000 Americans dead.

And a majority of Americans have now concluded the war was a mistake. However, President Bush strongly believes otherwise.

"The decision to remove Saddam Hussein was the right decision early in my presidency, it is the right decision at this point in my presidency and will forever be the right decision," said Mr. Bush.

Mr. Bush went on to vow America will continue to stand with Iraq. Yet with Americans still dying, pressure seems likely to mount to bring an early end to the war.