They already have eastern and western conferencesWithout Relegation and promotion there is no way the league can expand any further right? - you could do conferences I suppose but that seems odd for football.
I do get confused by the other tiers in the league, if there is no relegation or promotion what makes MLS > NASL > USL and if one grows stronger can it leapfrog the another.
I think one did leapfrog the other just recently. I'm sure they changed it so USL is the second level now, which I think lead to the NASL season being put on hold. I could look it up but I imagine somebody much more informed than me will give a better answer