I am working about the poem, The Star Spangled Banner by Francis Scott Key 1814. Why was the poem written?

During the night of September 13th, 1814 a poet-lawyer named Francis Scott Key sat waiting to return home after securing the release of a Maryland doctor who had been captured by the British. Because they were not able to return home until the attack ended Francis Scott Key sat and listened to the war, at Fort McHenry, which was too far away to see. Throughout the night he had heard occasional sounds of the fort's guns, but near morning the British attacks seemed less and less. He was beginning to wonder if perhaps the British had won. By looking out of a telescope he was able to see a large flag blowing in the wind. After only a few seconds he realized that it was the American flag, which had been raised as a sign of defiance to the British. He was so ecstatic to see that the fort had not fallen and that Americans were still winning the war he began to write a poem, later turned in to a song. When asked what inspired him to write such a song he commented, "Then, in that hour of deliverance, my heart spoke. Does not such a country, and such defenders of their country, deserve a song"..."