US President George W. Bush pledged Monday to ensure "an outcome that will merit the sacrifice" of those who have died in Iraq, offering both sympathy and resolve as the US death toll in the five-year war hit 4,000. "One day, people will look back at this moment in history and say, `Thank God there were courageous people willing to serve because they laid the foundation for peace for generations to come,' " Bush said at the State Department after a two-hour briefing on US. diplomatic strategy around the world. "I vow so long as I am president to make sure that those lives were not lost in vain." The president received another two-hour briefing earlier Monday at the White House on Iraq, this one from Gen. David Petraeus, the top commander in Iraq, and Ryan Crocker, the US ambassador to Iraq, via secure video hookup from Baghdad. Petraeus and Crocker are due to testify in Congress on April 8-9.