Seven years, seven long years.
In a brief moment of celebration at the discovery of Spartan-117, a thriving planet, and a friendly sentient life form, everyone rejoiced.
Then, shortly there after, catastrophe.
The Covenant, seemingly backed to their old size, made its return.
A small force of humans and Covenant Separatists helped the ponies in their defense of Equis, hopeful that they would prevail.
They failed.

But, though hope seemed lost, a light in the darkness appeared.
The Spirit of Fire arrived, just a day before the fall of Equis.
With the help of the Spirit of Fire, they were able to evacuate over 200,000 ponies before the Loyalists completed the glassing of the planet.

In the destruction of Equis and Equestria, Princess Luna, who is now the Captain of the U.N.S.C. , the one remaining Princess of the original two, agreed to sign a bill which allowed the ponies to join the U.N.S.C., which in turn allowed the ponies to help the humans and Separatists in their war against the Loyalists.
Since then, the humans and ponies have many achievements together.
With unicorn magic, combined with the humans advanced technology, many advancements in medical and military technology has been made.
Dr. Catherine Halsey has developed the Spartan IV's, which was made up of not only humans, but also ponies. These Spartans have been able to do feats that compares to the feats of the Spartan II's. Most notably Aqua Team, made up of three ponies named Sweetie Belle, Scootaloo, and Applebloom, who were able to take out three assault carriers by sneaking aboard the carriers and detonating Shiva class nuclear warheads inside them.

Sadly, since the U.N.S.C. is yet again fighting a losing war. Many planets that have been colonized since the aftermath of the first Covenant-Human War have been glassed, and the U.N.S.C. is yet again on the verge of destruction.
Hope is again fading, as the Covenant once again threaten the very essence of humanity, Earth. While light years away, the Covenant have discovered a new Halo ring, and are attempting to activate it.

It has been seven years, and now, it is life or death.