The Great War

The flag of Equestria flown during the Grand Galloping Gala.
~ Desigos

The Great War was a decades-long militarized conflict between two global superpowers, the pony nation of Equestria and an unnamed zebra nation with whom it shared a border. This war lasted multiple years and forced Equestria into a rushed industrial revolution as the two superpowers raced to outdo each other in the fields of arcane science, industry, and wartime technology.

One of these developments, the megaspell framework for amplifying the power of spells, was powerful enough that its use led to the destruction of much of Equestria.

History

Opening Hostilities

The most significant cause of the Great War was the rising number of trade sanctions involving natural resources between the two belligerent superpowers-- Equestria, which had a monopoly on magical gemstones, and the unnamed zebra nation, which had a monopoly on the coal needed to power Equestrian industry. As relations strained, minor conflicts broke out between the two nations. Eventually, the accidental massacre of civilians at Littlehorn Valley drove both superpowers into an all-out war.

Course of the War

In an attempt to end the war, the Ministry of Peace led a project along with the Ministry of Arcane Sciences in order to create the megaspell, a spell framework that exponentially amplified the power of any given spell, whether it be healing or devastating. The schematics for the megaspell framework were then clandestinely supplied to the zebra nation. This was done in hopes that the frameworks would be used to build immensely powerful healing spells that would, by preventing the deaths of anybody, guarantee a no-win scenario for either belligerent, and force everyone to stop fighting and come to the table -- the concept of Communally Assured Reciprocal Existence (CARE). 

Equestria eventually gained a significant technological lead over the zebras to the point where the milestones it needed to assure victory -- primarily bypass spells and alicorn mutations--had been reached, and mass deployment was mere weeks away. Seeing this, the zebras recognized that the war would not end in their favor and that defeat would be inevitable. Certain events and misunderstandings led the zebras to believe that Equestria was "under the influence of the stars" and would commit mass genocide and kill all the zebras should they win; with nothing left to lose, the zebras launched an all-out megaspell strike against Equestria.

The Last Day

Main article: Last Day

The megaspell onslaught lasted mere hours. The first city to fall was Cloudsdayle, which immediately resulted in the pegasi's abandonment of the war effort and their subsequent secession from Equestria. The next targets to be struck directly were Splendid Valley, Manehattan, Canterlot, and Fillydelphia. After this point, the pegasi raised a near-permanent cloud curtain over all of Equestria, blinding the zebras for the remainder of the megaspell assault and preventing them from acquiring targets with precision.

Aftermath

As expected, the megaspell onslaught devastated both Equestria and the zebra nation, ending the war almost immediately. In the wake of the war, the Equestrian government was completely annihilated, its civilian population largely decimated and the territorities it controlled reduced to swaths of irradiated wasteland. Equestria descended into a state of complete anarchy, and no organized civilizations rose from the ashes for many years to come. The majority of the surviving Equestrian population went into hiding in the hundreds of underground Stables that were constructed throughout the course of the war, and would only emerge sporadically throughout the centuries that followed.

The ultimate fate of the zebra nation is unknown, though it can be assumed that it suffered a similar, if not worse fate, as Equestria had far more megaspells,(which where far more advanced than the zebras) of their own and ample time to counter-strike. (the only known fact is that the zebra empires coastal regions and islands(where the ministry of magic believed that most of the zebra megaspell silos where located)) where utterly decimated "to the point where nothing will be able to live there for thousands of years" by the Celestia prime experimental solar megaspell.

Major events

• Big Macintosh sacrifice.
• Celestia's stepping down.
• Luna's reign.
• Creation of the Ministries.
• Megaspells.
• Last Day.

Time Line

• Start of the war.
• Massacre at Littlehorn.
• Celestia abdicates her throne.
• Luna reorganized a wartime Equestrian government.
• Creation of the ministries.
• Formation of the Shadowbolts by the Ministry of Awesome.
• First field test of a megaspell.
• Battle at Shattered Hoof Ridge.
• The zebras asked for a peace treaty in an attempt to assasinate Princess Luna, but instead they killed Big Macintosh who was guarding Celestia.
• Creation of magically-powered armor.
• Steel Rangers founded.
• Zebras "acquire" megaspell capability.
• Anti-material gun created.
• Assassination attempt on Applejack.