Tolkiens stories contain more symbolism than any other work. The things he has written stand for ancient legends and also for things that Tolkien and the people around him believed.
Eru Iluvatar=God
Ainur=Angels
Melkor Morgoth=Satan(once an angel, now evil)
Sauron and Balrogs=Devils
Gandalf could be any profet
In the days of Tolkien, people said that black people were 'evile =>southerlings
And sorry for the mistake that I've made but:
Mordor: unnown faction, if you look at the map you could say that it is Transsylvania, land of Dracula(Here we can see Tolkiens love for legends)
Southerlings= evil, black people
Easterlings= barbarians, steppe people that really want power= USSR(not my oppinion but Tolkiens)
Isengard=Nazi germany, industrialisation, using people who don't ask questions, murdering the people of rohan
Anduin= The Channel

Gondor= the land that is bravely defending the channel = Great Britain
Rohan= The jews, massacered by evil forces
OR Poland, France,... lands taken by evil forces
Note:These assumptions are never proved but even Christopher Tolkien thinks that his father meant it this way.