It is possible to made new units for Rhun? Wainriders - chariots cavalry
Wainriders
The Wainriders were a confederation of Easterling tribes who were united by their hate of Gondor, fuelled by Sauron. Following the Great Plague which weakened Gondor, they started their raids in 1851 of the Third Age and attacked in full force five years later, defeating the Gondorian army and killing King Narmacil II. They rode in great wagons and chariots (which gave them their name), and raided the lands of Rhovanion, destroying or enslaving its people. Gondor gradually lost all of its possessions east of Anduin, save Ithilien, to them. The thirtieth king of Gondor, Calimehtar son of Narmacil, defeated the Wainriders in battle on the Dagorlad, buying some rest for his land.
However the Wainriders struck back in 1944, allying themselves with the Haradrim of Near Harad and the Variags of Khand. They managed to kill King Ondoher and both his sons, but instead of riding on to Minas Anor and taking the city, they paused to celebrate. Meanwhile, general Eärnil of Gondor's southern army had defeated the Haradrim and rode north to defend his king. He came too late to rescue Ondoher, but managed to surprise and defeat the Wainriders in the Battle of the Camp. Eärnil was crowned king a year later. After this defeat the might of the Wainriders was broken, and their confederation collapsed.