I was with an alliance from the beginning and I kept growing till I surpassed all the ppl there with..

I was with an alliance from the beginning and I kept growing till I surpassed all the ppl there with most of them inactive, so I decided to quit, but then the leader contacted me and I'm trying to go back but I can't. Does the alliance's power level have to be above mine to be able to join? I don't even find it when I search in the alliances list.