The poetry of Walt Whitman, for instance, reflects scenes of the American Civil War which occurred during his lifetime.
In addition, figurative devices such as alliteration, assonance, metaphor, and simile are invariably used to layer these historical poems with expanding, enriching meanings.
A poet who writes historical poems can adhere to this ideal, but may also use artistic license to communicate ideas beyond mere fact, such as mythical or emotional truths.
Cleanth Brooks writes in The Formalist Critics: the author's intention as realized is the 'intention' that counts, not necessarily what he was conscious of trying to do, or what he now remembers he was then trying to doTo add to this, the purpose of a historical poem serves various ulterior motives.
One of these motives might include informing the audience at the time of present events, often to draw parallels and make a political statement.