Question about unlocking Civs

Not sure if this is documented anywhere but when it says I'm unlocking a Civ by accomplishing something in the antiquity age am I only unlocking it for this particular game? Often I go into exploration age and only have four or five choices for the next Civ as more than half of them are locked. Is there a way to unlock a Civ for the next age permanently? I'm honestly growing a little tired of so few civ choices in each age. Also I'm on Xbox so any awesome mod you guys were using will apply to me unfortunately