The most important chords in outlaw country music are the first, fourth and fifth chords of the key that the song is written in.  These are usually referred to by roman numerals as the I, IV and V chords.  If we take the A major scale, you will see below that these chords are A, D and E respectively;

            I          ii          iii         IV         V         VI        vii

           A         B         C         D         E         F^#        G^#

Figure 1

Figure 2

Figure 3