the song is about war and death.

"Make his fight on the hill in the early day
Constant chill deep inside
Shouting gun, on they run through the endless grey
On the fight, for they are right, yes, by who’s to say?
For a hill men would kill, why? they do not know
Suffered wounds test there their pride
Men of five, still alive through the raging glow
Gone insane from the pain that they surely know"

That is about fighting over land.

No Man Is An Island

No man is an island,
Entire of itself.
Each is a piece of the continent,
A part of the main.
If a clod be washed away by the sea,
Europe is the less.
As well as if a promontory were.
As well as if a manner of thine own
Or of thine friend's were.
Each man's death diminishes me,
For I am involved in mankind.
Therefore, send not to know
For whom the bell tolls,
It tolls for thee.

— John Donne

These famous words by John Donne were not originally written as a poem - the passage is taken from the 1624 Meditation 17, from Devotions Upon Emergent Occasions and is prose. The words of the original passage are as follows:

John Donne
Meditation 17
Devotions upon Emergent Occasions

"No man is an island, entire of itself; every man is a piece of the continent, a part of the main. If a clod be washed away by the sea, Europe is the less, as well as if a promontory were, as well as if a manor of thy friend's or of thine own were. Any man's death diminishes me, because I am involved in mankind; and therefore never send to know for whom the bell tolls; it tolls for thee..." 

Have you read the poem?

 It means that we are all in "it" together, if one gets cut, we all bleed. If the waters  get poisonous, we all die.

 It means that everything in the universe is connected, fragile yet strong, looks muddled up but really is clear if you are looking at it from the correct vantange point.. It means if someone yells out "Help me, Help me!!" as they are throwing themselves into the raging river to save a child, you don't hesitate or call for he;p on your cell, you jump in to help them both survive. Hopefully, when all of you are on the shore and the crowd draws, you slowly seperate yourself from them, keeping who you are and what you did to yourself because that is not why you did it, You did it because the bell was tolling and you were the one who heard it ring.