What is the "battle" in "Range-finding" by Robert Frost?

Robert Frost's poem "Range-finding" is about a stray bullet from a battle that, on the way to its target, travels through nature. The poem begins, "The battle rent a cobweb diamond-strung / And cut a flower beside a ground bird's nest / Before it stained a single human breast." The "battle" could be any military conflict, but as the poem was written in 1916, it is most likely a battle that takes place during World War I. In the poem, a bullet from the battle tears a cobweb and cuts a flower on its way to lodge itself in a human chest. The flower droops over, but a bird goes on visiting its young. The poem is about the ways in which events in the human world--in this case, a battle--affect the natural world. It is also about the ways war causes collateral damage--in other words, damage that is not the war's original target. This was very relevant at the time Frost wrote the poem, as World War I caused a great deal of collateral damage and hurt civilians as well as soldiers.