max troops allowed in mines?

I had occupied a lvl 1 mine. after occupying it, I built more cats and my cat count increased to over 16k. when the mine prestige began to decay, I abandoned the mine and then tried to attack it again. to my surprise, I got a system message that I could not occupy the mine. at first I thought that perhaps this was because someone else had beat me to it (attacking mine), but 15 minutes later the mine was still unoccupied and the system still wouldn't let me attack. is there a max troop level beyond which you are blocked from occupying a mine? if yes, what is the max for each lvl?

nvm. I just found the answer. after occupying the lvl 1 mine, I upgraded my alliance to a lvl 3. apparently there is a min lvl that you can attack. for a lvl 3 alliance, the min mine lvl is 2.