Since 1988, the National Trust for Historic Preservation has used its list of America's 11 Most Endangered Historic Places as a powerful alarm to raise awareness of the serious threats facing the nation’s greatest treasures.  This year, the Trust celebrates the 20th America's 11 Most Endangered Historic Places list as one of the most effective tools in the fight to save the country’s irreplaceable architectural, cultural and natural heritage. The National Trust 2007 America's 11 Most Endangered Historic Places List announcement is Thursday, June 14. [ backgrounder | press release ]