As it has been said, Summoning takes his inspiration in Tolkien's World, and precisely in the Middle-Earth. It is not easy to sum up this world, described in several books (The Hobbit, The Lord Of The Rings, The Silmarillion, Unfinished Tales, the Book of the Lost Tales, for the most famous), but i will try.

=>> 1°/ The World and its Creation
=> At the very beginning, there was nothing. Only Erù, the powerful, also called Illuvatar. Then he created the Ainurs, or Valars, and asked them to compose a symphony for him. His favourite Valar, Melkor, the best of them all, wanted to rebel and create a more beautiful symphony. Then happened a musical battle, in which Melkor finally lost. This was more or less forgotten, but not by Melkor who then hated Erù and his creation.
One Day, Erù showed to the Valars the physical representation of what they created : Ëa, Arda, the Earth. It was so wonderful that some of the valars wanted to stay in. Erù allowed them, but told that the planet would be used to host his two children.. Then some valars, and their helps the Maias went to Ëa, amongst who Melkor. Each valar got specialized in which he liked most : Ulmo, valar of water was in everything that was liquid and pure, for example. And Melkor got specialized in hatred and destruction ; each time a valar created a mountain, he created a crack, and so on, that is why the world did not get as marvelous as it was expected to be.

=>> 2°/ The Diferents Races
=>As Erù wanted to create his two children, some valars wanted to do so. The valar of the mountains created the Dwarves, but when Erù knew that, he condemned them not to see the daylight before the first-born, this is why they lived in caves and caverns. The valar of the trees understood that her forests were threatened by the dwarves, and spoke with Erù, who finally allowed her to create her own race, the Ents.
At last, came the first-born, first children of Erù, the Elves. They appeared in Middle-Earth, and Melkor, who discovered them first, wanted them to attack the valars, but this treason failed ; when the valars found them, they wanted to take them in their kingdom, at west of the great see. Then started the Elf exod : some wanted to stay, some stopped during the journey, but finally some got in the valar territory.
Then lots of things happened : Melkor were searched, found, emprisonned, and he repented. He could live with Elves and Valars. Again he made everyone hate each other, fled, and the Elves left the kingdom to make him war. At that time Melkor were called Morgoth, which seems to be a nasty nickname.
Then arrived the Humans, the second-born, second children of Erù, who had made them a present : death ! Indeed, while Elves woke up in valars' kingdom when dead (but then they could not manage to come bak to Middle Earth), nothing permetted to know were humans were sent after their last breath.
Melkor made them war, because jealous. He did not have the power of creating, only changing. When in the valars' kingdom, he had darkened numerous souls, and so he did when he went to the Middle Earth. With Elves his made Orcs, with Ents he made Trolls, and darkened Maias were called Balrogs ; the most famous one became his lieutenant : Sauron.

=>> 3°/ 1st and 2nd Ages
Sum up : Elves, Humans, Dwarves (main races, whose origins are known), and Orcs are in Middle Earth (forget Trolls ans Ents, who have a little play). there is also Melkor, Sauron, and their 'bodyguards', the Balrogs. At west are Valars (and Maias). There happen lots of stories told in the Silmarillion and Unfinished Tales. It's are told how were created the Silmarils, who kept the greatest light, how they where robbed, found, lost.. Melkor were taken and disappeared.
Second Age : Sauron got some Power, seemed to bend before the men, and learn with them. Then he created and darkened the rings. He is finally outwitted, and the Lord of the Rings is lost.
This is really sum up since it is a long time i've read this, and i did not get really interested in that period : i am more a Third Age Historian ;)

=>> 4°/ 3rd Age, the Middle Earth : Summoning
This is the period which interest us, since it is when happen the facts described in the LotR, and when, i think, Summoning date their songs.
The earth have changed between the 2nd and 3rd ages, this is why the maps are different.
houba
Lots of things happen in this ages, and here is the situation at the beginning of the LotR :
The ring found by Bilbo in The Hobbit, were given to Frodo, his nephew. Bilbo went to Rivendell to live his lasts days. We soon understand that this ring is the master ring, Sauron's one, the most powerful, whith which sauron could manage to rule the Middle Earth, for a first step. He is looking for it, and Frodo has to flee and wants to reach Rivendell, were the wise Elves are, to give them the ring. But all will get very complicated..
This is a small sum up since i don't want to give you any important information, but i will soon make a better explanation of middle earth à that age.
Please read the book and feel Tolkien in your vein before going to see the film :'(