I wasn't sure if I should rate this P or PG, since there is only mention of darkness/evil and subtle mention of violence. This poem isn't about flowers or ponies or anything like that, so I guess it gets a PG rating.
But, regardless, here it is -- The Last March of the Ents:
A power greater
From the earth
Was aroused that night
Force and strength
Which had lain still
Now rose again in might.
Asleep they lay
For countless years
Their power was withheld
And now unleashed
With reckless force
And livid rage did wield.
A silent wood
Where all was still
And suddenly came fast
An army great
A legion tall
To slay their foes at last.
Their march was slow
To Isengard
Where death and evil lay
But drums beat loud
And steadily
Ever forward on their way.
But only evil
Great as this
Would awake such wrath
Only death
So deep and dark
Would stir the march upon that path.