As tens of thousands gather at Gettysburg this summer to watch and recreate the battle fought 150 years ago, area exhibits, monuments, and historic sites are reminding Philadelphians of a traumatic time that left its mark on the city. "After Washington, the Northern city most impacted by the war was Philadelphia," said Andy Waskie, a historian and Temple professor who wrote Philadelphia and the Civil War - Arsenal of the Union. "It was the most important center of the war effort, and if it had been removed from the Union, it would have been a tremendous loss,” he said.