War for Sake of the Elves

Background
Through the use of spies, Melkor discovered the Elves first as the Valar were busy in their realm in Aman. When the White Horseman arrived, many of the Elves had been tricked into believing that he was an enemy and fled. Those who wondered too far from home were captured by Melkor's dark servants and taken to Angband and Utumno where they were tortured and corrupted until they became mindless servants who lived only for war. This was the most hateful act to Eru because it destroyed the most beautiful creatures on Arda and corrupted the surviving elves into orcs.

Prelude
After the Dark Lord Morgoth sought to claim Middle-earth for his own. He built a massive fortress known as Utumno in the North of Middle-earth, (at this time known as Arda) but not before the Valar knew of his evil crimes, such as corrupting Arda with his evil creatures and corrupting the hearts of all sentient creatures, but perhaps the crime which inspired the Valar to action was the creation of the Orcs. The Orcs spawned forth from the Earth like wolves and devoured whatever thing they came upon. Manwë and the rest of the Valar could stand this no longer, since Eru couldn't bear to see his children being tortured by the dark powers, and so the Valar took counsel with each other and decided to rid Middle-earth of his tyranny.

The War
They declared war on him and came to Arda in physical form with presumably a massive army of light and battled him for many decades in the counting of the Sun. The Host of the Valar easily defeated Melkor's host at the the Battle of the Powers in northwestern Middle-earth. The remnant of his forces fled back to Utumno and fortified themselves there. The Valar passed over Middle-earth and placed a guard over Cuiviénen to protect the elves from any further effects of the war or perhaps from an attack from Melkor's servants. Then, the Host of the Valar went north to Utumno and besieged it. After decades of siege, the Host of the Valar finally broke through and after Tulkas himself personally defeated Melkor in combat, they captured him and took him to Valinor for judgment, and sentenced him to prison in the Halls of Mandos for thousands of years.

Effects on Middle-earth and Aftermath
The war between the two powers devastated the lands of Middle-earth and the face of the continent was changed. The distance between Middle-earth and Aman separated by the Great Sea became wider. A Gulf in south was created and small bays appeared between the Great Gulf and Helcaraxë. The Mountains of Hithlum and the highlands of the Dorthonion were created. The Sirion river that flowed into the newly formed Bay of Balar appeared. Free of evil, the elves were invited to Valinor and undertook a Great Journey across Middle-earth in which new Elven cultures were developed. The result was the peopling and colonisation of the western parts of Middle-earth with the Children of Ilúvatar.

Legacy
The main legacy of war was that it allowed the Elves to go to Aman and Valinor where they became High Elves, enlightened, cultured, and skilled. Elves in Middle-earth established themselves learning much of nature, woodlore, and shipbuilding. However, the fear brought about by Melkor caused some elves to relent and stay in the east longer. These elves, the Avari and the rest of the Dark Elves developed separate and more secretive cultures and stayed away from the affairs of their long loss brethren for the most part. They would then thousands and thousands of years later in the Third and Fourth Ages become the Wood-elves that would be the last of the kindreds of left in Middle-earth ever after. The languages of the elves spread throughout Middle-earth and blended and influenced other tongues and became known of ever after.

The other legacy was that Melkor, then released from prison who would ever after remember that his downfall was because of the Elves sought revenge thus causing the Revolt of the Ñoldor and The War of the Great Jewels and the battles and dramas that followed. It would also serve to shape the course of the history of the Children of Ilúvatar for ages to come.