For thousands of years Equestria has been happy and away from any type of harm or unhappiness. The only type of unhappiness came naturally such as fires, earthquakes, floods, etc.. But all of the events had one thing in common, they weren't permanent. But their was one word that got the best of everypony, Death...
No pony ever wanted to hear or face Death after seeing Death take their loved ones. But of course, the two alicorn princesses were the only ones who would never face death, but they would have to deal with the fact that others would... Death was the one thing both princesses feared most and they wanted to deal with it as least as possible. So they tried to make Equestria as safe from any type of harm, and they succeeded. But the one thing they could not get rid of, the Everfree Forest... It was covered in a magical essence from all the animals that lived in it that not even the princesses could relieve, so they just quarantined it off from Equestria. But either way they were safe from harm.
Although, everypony came to that stage in their life where they would have to die naturally. It was a peaceful way to die, but it still caused pain to the ponies that they loved. But one day the two princesses realized that when any type of pony dies, it releases a unused magical essence that comes straight from the dead soul and disappears into nothing. The essence ran on pure happiness and joy. But the essence was also strong and almost, alive...
Then one day, the princesses devised a plan. They conjured up all their energy and cast a spell upon all of Equestria. Now whenever somepony dies, it's magical essence goes into the mind of all the ponies who knew it and blocked off the memory of that ponies death. But there was a catch. You generate the energy every second of your life but only had enough when you were an old age. But it was no problem since everypony lived to that age. So in a way Death no longer existed.
As it does now, Equestria lives in harmony and nopony has any worries or problems at all. Years passed and everypony stayed happy and never encountered sadness at all (Other than the ponies that lived to during the reign of Nightmare Moon). Equestria was truly experiencing harmony. Little did anypony know that would all change one fateful night...