5.14Why ii–V–I matters so much

Take the last three chords:

Dm → G7 → C

or:

ii → V7 → I

This is one of the strongest functional progressions in tonal music.

Why?

Because each step has clear harmonic direction:

ii prepares

V7 creates strong tension

I resolves

In jazz, these are usually seventh chords:

Dm7 → G7 → Cmaj7

This is the famous:

ii–V–I