A friend of mine, Dave Stone, has written numerous songs about historical events in the Halifax and Nova Scotia area.

From what I understand of his process:
Typically he gets inspired, will start writing something down. Next he starts doing research. LOTS of it. He'll read all the historical facts about the event(s) from books written about the subject. If he can, he'll go look at the primary sources during this research. People who lived through it are some of his best sources.

Then he'll start crafting the song(s) which come out of the process of learning. He'll see some quote by someone, and that puts a picture in his head, and he'll write 4 or 6 verses. He'll read something quite compelling, and filter it down to 6 or 8 verses. After several iterations, it gets to a reasonable song length.

Case in point, he was at the Stan Rogers Folk Festival in 2003. During the week leading up to it, they held a series of song-writing workshops. In one of them, he was paired with Ron Hynes (yes, THAT Ron Hynes!). The teams were given some information about the local area, including some of the history and legends. One of them, about a young girl, struck a chord with the two of them, and that afternoon they came up with this song Anna Maria

It's quite touching. Dave has quite a number of historical songs. HAve a look at some of them

Birth of a Queen - Bluenose
Down Through Halifax
Halifax Explosion

Enjoy now.