Why should we not wage wars against each other? (Please refer to the poem "No Men are Foreign.")

The idea that we should not fight one another is the basic
message of this whole poem.  So, to find the answer, you simply need to look at the
arguments Kirkup makes.  The best place to find these arguments is in the part of the
poem up to line 12.

Basically, Kirkup is saying that we are
all brothers -- that all people are alike.  He says that we all walk upon the same earth
and we will all be buried in that earth when we die.  He says that all people share
common goals and hopes and dreams.  In these ways, we are all alike.  Because we are all
alike, it would be perverse to fight one another.  It would be as if we were fighting
ourselves.