US President George W Bush marked the fifth anniversary of the beginning of the war on Iraq Wednesday by acknowledging the "high cost" of the conflict but vowing US forces will prevail, according to dpa. "We will accept no outcome but victory," Bush said in a speech at the Pentagon. "I reaffirm the commitment. The battle in Iraq is noble, it is necessary and it is just. And with your courage the battle in Iraq will end in victory." Bush said his decision to invade Iraq in March 2003 has left the United States safer and world better off because Saddam Hussein can no longer slaughter Iraqi citizens, threaten Iraq's neighbours or compensate the families of Palestinian suicide bombers. The war in Iraq in recent years grown unpopular with the US public and contributed to low job approval ratings for Bush, whose historical legacy will be based on the outcome of Iraq. More than 3,900 US soldiers have died in a fight that has so far cost US taxpayers more than 600 billion dollars. "Five years into this battle, there is an understandable debate over whether the war was worth fighting, whether the fight is worth winning, and whether we can win it," Bush said. "The answers are clear to me. Removing Saddam Hussein from power was the right decision, and this is a fight America can and must win." Bush tied the war in Iraq to the broader fight against terrorism, warning that an American pullout would allow al-Qaeda to gain a stronghold in Iraq to carry out worldwide attacks and pursue its desire to acquire weapons of mass destruction. "Defeating this enemy in Iraq will make it less likely that we'll face the enemy here at home," Bush said. The war in Iraq began on March 20, when US warplanes carried out a strike in Baghdad on a building suspected to be housing Saddam Hussein. US troops marched onto Iraq soil from Kuwait the following day and within less than a month Saddam's regime collapsed. Saddam went into hiding before his capture in December 2003 and eventual execution by the new Iraqi government in 2006. The quick toppling of Saddam's regime did not result in the speedy transition to democracy and self rule the Bush administration had hoped for as a resilient insurgency took hold and al-Qaeda began launching spectacular and deadly attacks. At the same time, Iraqi civilians went to the polls to elect a government in what was seen as a historic achievement in the Middle East. But that government has been ineffective at overcoming the ethnic and religious divide between Sunnis, Shiites and Kurds and has struggled to pass key legislation to end the ethnic tension. The ethnic divisions in Iraq brought violence to a peak in 2006 and early 2007 as sectarian killings sharply increased, bringing the country to the verge of full-blown civil war. Bush responded by expanding the US presence in Iraq from 130,000 troops to 160,000 in what has become known as the "troop surge." Since the surge began, Bush said, violence and sectarian killings have dropped along with the death rate of US troops as thousands of al-Qaeda and other extremists in Iraq have been captured or killed. "The surge has done more than turn the situation in Iraq around," Bush said. "It has opened the door to a major strategic victory in the broader war on terror." Bush warned, however, the United States must remain in the fight to build a foundation for Iraq's future based on the progress that has been made since the troop buildup come into full for force last summer, and warned an early withdrawal could plunder Iraq back into chaos. "There's still hard work to be done in Iraq. The gains we've made are fragile and reversible," Bush said.