Please try purge and reinstall.
Purging game installation
Please uninstall GC3 from Steam by following the instructions below.
STEAM: Right click GC3 in your Steam library and select "Uninstall..."
After GC3 has been uninstalled, please press the Windows key and "R" at the same time. In the window that appears, paste the path below and hit enter:
%userprofile%\Documents\My Games
In the "My Games" folder, if there is still a folder remaining called "GalCiv3" (or "GC3Crusade") please rename it so a new one will be generated.
Once again, press the Windows key and "R" at the same time, and use the path below:
%programdata%\Stardock\
You should see a folder named "Galactic Civilizations III", please rename this as well.
Lastly, please navigate to the path below and delete the entire folder for GalCiv3:
STEAM: C:\Program Files (x86)\Steam\SteamApps\common\Galactic Civilizations III
Note: The path above assumes you've installed GC3 to the default Steam directory. You may need to adjust the path accordingly if it is installed to a non-standard location.
Restart your computer and reinstall GC3 using Steam. After it has completed the installation, please create a new save and let us know if you experience any further issues.