The series is largely based on historical events.

There were three Goryeo-Khitan Wars. The series clarified that it started in 1009 during the rebellion; and in 1010 was when the Khitan Empire / Liao Dynasty invaded Goryeo again.

This is correct as far as historical records go:

• 2nd Goryeo-Khitan War: 1010 and 1015-1017.
• 3rd Goryeo-Khitan War: 1018 to 1019.

The king was only recognised, and permanent peace between the two dynasties was formally agreed, in 1022.

It is not yet clear if the series will cover the 3rd Goryeo-Khitan War and the 1022 recognition of the king. This is the current understanding as far as the focus of the story goes, which are the king and General Kang Kam-Chan. But, it could very well be that they'll only focus on the 2nd Goryeo-Khitan War up to the last episode (episode 32). And the 3rd Goryeo-Khitan War will probably be a 16-episode Season 02.

Let's just adjust it accordingly as more information becomes available. Unless someone already have solid information up to what year Season 01 will cover.

Also see: Goryeo–Khitan War