Angolmois: Genkou Kassenki

These are two shows that have lots of similar story elements and themes. Both are about people trying to survive and fight a war in a land that is not their home. Battles between armies, warships, sword-fights, and tactics. I would argue that everything Angolmois does, Vinland Saga does better, especially when it comes to characters, but both are still enjoyable if you are looking for a historical war series.  

Both are historical action. In both main protagonist has once been a famous warrior, but then quit due to some unfortunate circumstances. Both were summoned again to join a war. And both eventually had to lead an army to protect his country or his people.  

There's something about the mood of these two that is sometimes similar. Golden Kamuy has a lot more humor, but both have entertaining battles that often involves the terrain/forest around them. If you are looking for superficial similarities, both main characters have scars on their faces and are good in a fight. 

Both are about ancient war and battles 

-historical -war/conflict -violent  

Both very underrated samurai shows.Badass and intelligent main characters. Very realistic characterizations and mature content. Both shows contain plenty fighting scenes.Angomois focuses on the action while Onihei on the mystery. 

-A group of highly characterized misfits gets in over their head fighting a war they didn't expect to be involved in -Heavily rooted in classic themes of honor and tradition, and whether they should be ignored at times -Small party has to use ingenuity and guile to outwit an opponent that outmans and outguns them 

Both are focused heavily on military tactics and surviving in less than favorable conditions. Groups of characters that are cast from their home and have to survive/fight in another land. Arslan has more character development, though both are plenty enjoyable if you just want a military action romp. 

Both are about Japan's historical incidents, they follow a character and their struggle to protect the people in the area. Both struggle alot for being outnumbered and face the deaths of many of their comrades. both have their weird sides as well.