The Great War 5.0 - Installation Guides
If you're having trouble getting the 5.0 launcher to work, here are two alternative installation guides that help you through the manual install option.
Update: with 5.1, we extensively tested the launcher using our proud army of beta testers before releasing it. If you for any reason still encounter launcher issues, this guide should solve your problems: however bear in mind that it was intended for a complete uninstallation and reinstallation of 5.0, and that some minor details may have changed with 5.1 (but the guide should still be completely compatible).
Video Installation Guide - by Point_Man
Easy Step-By-Step Alternative Installation Guide (with images!) - by Aanker