In the game settings, the maximum resolution is 1600×1024. Through the settings file, you can change to 1080p or whatever you want.
In the folder with the game we find the file along the path Ancient Wars – Sparta \ Profiles \ Profile01 \profile.ini, open with any text editor and find the lines:
ResolutionX 1920
ResolutionY 1080
and then write the screen resolution you need.
To complement Fate of Hellas slightly different layout:
In the game folder, find the file along the path Fate of Hellas \ Profiles \ TheFateOfHellas \ ProfileXX\user_profile.up, open with any text editor and find the lines:
options.video.width 1920
options.video.height 1080
and then write the screen resolution you need.
