When did Francis Scott Key write the poem that became the National Anthem?

The morning after the battle of York, July 4, 1815

July 4, 1814

The night before the battle of Fort McHenry, September 14, 1814

The morning after the battle of Fort McHenry, September 14, 1814

Step-by-step explanation:

He wrote it the morning after the battle of Fort McHenry, September 14, 1814

The poem was originally called " The Defence of Fort McHenry " and he wrote it after he saw Fort McHenry being bombed. The morning after the battle, he was inspired by the sight of a lone U. S. flag still flying over the fort at daybreak.

On September 14, 1814, Francis Scott Key pens a poem which is later set to music and in 1931 becomes America's national anthem, "The Star-Spangled Banner." The poem, originally titled "The Defense of Fort McHenry," was written after Key witnessed the Maryland fort being bombarded by the British during the War of 1812.