If you want to play with more than 18 Civs on a Mac, you will need to run the Windows version of CIV in a virtual computer running on your Mac. Wine, I believe, is a free but complicated way to do that. I run Parallels, a commercial program that is not too expensive, on my Mac, in which I run Windows 7. Of course, you would also have to purchase a Windows OS. Among other programs that I need to run now and then under Windows, I have CIV BTS installed there as well, which enables me to run any of the mods that don't work on MacOS.