Stronghold HD uses "gameranger" to provide multiplayer functionality. Refer to the following article for information:
Gameranger requires DirectPlay, which is not installed by default on Windows 10.
To install DirectPlay on Windows 10...
Either:
- Go to Control Panel
- Click "Programs"
- Click "Turn Windows Features on or off"
- Expand the "Legacy Components" branch and tick "DirectPlay"
- Click "OK".
- Wait for a while for your PC to finish with everything, and the PC will need to reboot as well.
Or:
- Open "Settings"
- Click "Apps"
- Scroll to the bottom to find the "Related Settings" heading and click "Programs and Features"
- Click "Turn Windows Features on or off"
- Expand the "Legacy Components" branch and tick "DirectPlay"
- Click "OK".
- Wait for a while for your PC to finish with everything, and the PC will need to reboot as well.