Major scale modal chord progressions are built from the seven note major scale. The scale on which a chord progressions is built constitutes the key.
The tonal center of the chord progression is where the ear hears the resolution point of the progression...which means the tonal center is also the modality. There are seven tonal centers in the major scale and chord progressions can be created to resolve to any of those seven scale degrees.
Each mode has its own characteristic flavor, and you'll start to hear the effect this has when you are improvising or composing ideas of your own.