How does o. henry's use of third-person narration in "after twenty years" affect the story?

The use of third person narration allows the author to tell the story from the perspective of what is seen and done and not what the character think or thought. This narration style helped the author to effectively handle the surprise climax at the end of the story.

On August 24, 1814, during the War of 1812 between the United States and England, British troops enter Washington, D.C. and burn the White House in retaliation for the American attack on the city of York in Ontario, Canada, in June 1812.

When the British arrived at the White House, they found that President James Madison and his first lady Dolley had already fled to safety in Maryland. Soldiers reportedly sat down to eat a meal made of leftover food from the White House scullery using White House dishes and silver before ransacking the presidential mansion and setting it ablaze.