Well i have this issue too like 50% of the people that play civ, its amazing no one else complains about this more.
Perhaps ive been a little more rigorous that most in attempting to fix this issue.
I can tell you what it isnt at least, anything the support desk tells you it could be. so its not gfx drivers, its not audio set to 4100 + nor is it outdated directx or .net framework or vc. Neither has it anything to do with your network connection.
Ive reinstalled my pc several time, after the support desk claimed it "must be my pc". I literally installed windows, the gfx driver and steam/ civ and gave it a go. And it still crashed. i tried windows 7 windows 8 and windows 8.1 all crash when hosting for some reason.
Now recently ive been testing with windows 10, and to my surprise it has several issues, but crashing while hosting is not one of em!. It runs slower between turns, it freezes when you alt tab (on build 10049). But ive done 5 full games for hours with lots of people quitting and no resyncs and no crashes or freezes.