I also have the same problem of the game freezing at the end turn.....it is random....it can occur at any date.....and at any faction during the ai's cycle through.

But,all is not lost,if you have a little patience,the third time it happened to me,i got upset and decided to go get something to eat,without doing anything to the game,i just let it sit there frozen,i came back 20 minutes later and it was unfroze and at the beginning of the next turn.

it seems to me the ai gets stuck in some sort of loop,yet,eventually gets out of it,it can freeze from 5 minutes up to 15 minutes,but,always comes out of it

I don't know if this is the case for all computers,all i know is that it unfreezes on mine and that it only started freezing during the end turn when i installed the new patch 1.2

Also,it will freeze more than once,i found that after every three or four turns it freezes again,but,eventually gets through the end turn