=> Both are long historical sageuk dramas with many episodes from the 2000s
=> Both dramas are set in Three Kingdoms Period
=> Both sageuk dramas got high ratings in Korea and was even aired in some international countries like the Philippines
=> Both main characters have at least two love interests (fans of both dramas still debate which love interest is better for the main character)
=> Both main characters have to overcome obstacles/prejudices to become a worthy ruler.
=> Both have many cool fight scenes
=> Both have actor Jung Ho bin (In Jumong, Jung Ho Bin plays Wootae, Soseono's bodyguard. In Queen Seon Deok, he played Munno, a great martial artist who is also Bidam's master)

=> Kingdom of the Winds follow Jumong's grandson
=> Song Il Gook is the male lead in both dramas (and he plays kings in both)
=> Both are stories of young men who trained and have to grow up to become a great King

Both are dramas about the founding of nation/dynasty. Both main characters in this drama eventually became kings. Epic dramas with lots of epic fight scenes. There are at least two women loving the male leads in this drama.

Both are sageuk by the same writers. Shin Se Kyung is in both dramas too.
For Arthdal fans, you might want to check 6 flying dragons for Shin Se kyung acting . 6 flying dragons was a great drama that won many awards.

Now that season 2 is confirmed with new actors, I'm sure fans of the replacements will watch season 2 for them. it is absolutely necessary you watch season 1 because it is quite a complicated world and the worldbuilding is in season 1. I also hope for some appreciation for the efforts of the season 1 cast (I'm saying this seeing how most people underestimated Arthdal season 1 drama when it was airing).
Now, if you notice the drama, it is presented in many titles. If you wonder why is that, the season 1 of the drama is divided into three parts. But all three parts comprised of season 1. This particular part here is part 2.
I also recommend season 2 for season 1 fans. Please watch the drama even with the cast change.

Now that season 2 is confirmed with new actors, I'm sure fans of the replacements will watch season 2 for them. it is absolutely necessary you watch season 1 because it is quite a complicated world and the worldbuilding is in season 1. I also hope for some appreciation for the efforts of the season 1 cast (I'm saying this seeing how most people underestimated Arthdal season 1 drama when it was airing).
Now, if you notice the drama, it is presented in many titles. If you wonder why is that, the season 1 of the drama is divided into three parts. But all three parts comprised of season 1. This particular part here is part 1.
I also recommend season 2 for season 1 fans. Please watch the drama even with the cast change.

Both are the works that show the political rivalry of Grand Prince Suyang (later King Sejo) and Kim Jong Seo.

=> Both works are about King Jeongjo
=> Han Ji Min is in both but her character in Fatal Encounter is not as nice as her character in Yi San.

Similar to the other recommending these two dramas to each other, I'm also gonna mention how the two works are connected by the fact that the students in Sungkyunkwan Scandal are helping in clearing Cown Prince Sado's name. This is because Crown Prince Sado's son Yi San/Jeongjo is the king in Sungkyunkwan Scandal.
Another interesting connection is how Yoo Ah In is in both works. For The Throne fans, they'll see Yoo Ah In's breakthrough project. For Sungkyunkwan fans' they'll see the Yoo Ah In sageuk movie that brought him awards as well as the first among his movies to be submitted by Korea for the Oscars.

=> Both are high profile sageuk projects starring Yoo Ah In
=> Both were shown in 2015 (Six Flying Dragons ended in 2016)
=> Yoo Ah in won many awards for his portrayal in both sageuk projects
=> Yoo Ah In's role has a similarity in both dramas, he's someone who doesn't obey his father's wishes.
=> Because of the success of these two projects (along with Yoo Ah In's 2015 movie Veteran), 2015 was called "A-in-shi-dae" (Ah In era).

I recommend Dong Yi for The Throne fans since it gives character to the mother of King Yeongjo, the woman who was only mentioned as a lowly concubine in The Throne. Dong Yi is the love story of Yeong Jo's parents as well as the political happenings during Yeongjo's father King Sukjong's era. Dong Yi also shows the rivalry between concubines including Dong Yi (Yeong Jo's mother) and Jang Ok Jung (mother of Yeong Jo's brother, who was the king before him as mentioned in the drama). Through watching Dong Yi, the audience will understand why some people in The Throne think King Yeong Jo killed his brother for the throne as well as how Dowager Queen Inwon was Queen Dowager despite her not being King Yeong Jo's mom.
For Dong Yi fans, The Throne movie shows one tragic aspect in the long reign of Dong Yi's son Yeoning aka Yeong Jo: the events that lead Yeong Jo to put his son Sado in a box which led to his son's death.

In both Jang Ok Jung and The Throne, we see Yoo Ah In playing a Joseon Royal. King Sukjong (Yoo Ah In's character in Jang Ok Jung) is also one of the main characters in Jang Ok Jung. This means that Jang Ok Jung is a show that might be enjoyed by The Throne fans since it has both Yoo Ah In plus the audience get to know more about King Sukjong (who is only barely mentioned in The Throne). One must keep in mind that Jang Ok Jung has a little twist in that it tends to be more sympathethis towards Sukjong's concubine Jang Ok Jung, who is more historically known as the more villainous concubine. Jang Ok Jung is the mother of the brother of Prince Sado's father, King Yeongjo.