Ok So there are two ways to play this song.

I saw one way that has a C#m in it and that is unnecessary! The basic chords to this 
are:

A, D, and E

The first way to play this song is to play these chords either open or with bar chords 
chords sound better, in my opinion):

Intro: A (for two measures), D, E      x2

           A  D E
If I had a hammer
                 A  D E
I'd hammer in the morning
                  A   D
I'd hammer in the evening
              E
All over this land
              A
I'd hammer out danger
                 D (or D7)
I'd hammer out a warning
               D     A         D               A
I'd hammer out love between my brothers and my sisters
D  E          A D E
All over this land

End: A D A.

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The second way is with a capo on the 2nd fret:

Intro: G (held for two measures), C, D   x2

           G   C D
If I had a hammer
                 G   C D
I'd hammer in the morning
                  G   C
I'd hammer in the evening
              D
All over this land
              G
I'd hammer out danger
                 C
I'd hammer out a warning
               C     G         C               G
I'd hammer out love between my brothers and my sisters
C  D         G  C D
All over this land

End: G C G.

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Either Way is easy and sounds good. I have performed this song with a friend of mine 
the second way and me using the first. Listen to the song for strumming and phrasing. Have 
Comment with comments (haha) or correctins. :]