ii V I IV in G Major

The heavily-used ii V I IV progression extends the ii V I progression by moving the the 4th Chord after the I.

Since this progression is in the key of G Major, but starts with an A Minor chord, this can also be referred to as being in A Dorian.

Since this progression is in the key of G Major, but starts with an A Minor chord, focusing on the A note at the beginning of the progression makes sense. If we play the G Major scale (A,B,C,D,E,F#,G), but instead of starting with G, we start with the 2nd note, A, this is known as the A Dorian Mode.

G Major Scale (2 options):
G Major Scales
A Dorian Mode (2 options):
A Dorian Modes