FF I, what exactly happened? (SPOILERS)

[Flashback007]

Every thing is now ok, so answer

I like playing FF I, but one thing keeps bothering me. What happened? Ok, I can follow it till the part that the Sages go explain what happened

400 years ago, we lost control of the winds, 200 years later, we lost the water, the Earth and Fire followed. The power that binds this world are gone.

That doesn't make sence for me, why does the fiends not come together but single. It says so, first Wind, then Water, Earth and finnaly Fire. If could come single why not with a few days difference. Now with a few years difference. That doesn't make any sense to me. Later in the game we find out that it is Garland that has been sending the Fiends towards the future (he lives in the past) with the help of the black orb. So maybe he decide to put those Fiends in different times? But why? And why? So we encouter Garland later in the game as endboss. Then this happens:

Remember, me Garland? You puny tought it had defeated me, but the Four Fiends send me 2000 years in to the past. From here I send the Four Fiends to the Future. The Fiends will send me back to here and the Time-Loop wil go on. After 2000 years I will be forgotten and the time-loop will close. I will live forever and you will meet your doom

So basicly what he says (I don't have any quotes from the Origins version, maybe they are the same, but post them please) is that after your party has beaten him, the Fiends from the past somehow managed to get him to their age. When he was all cured etc he send the Fiends as a thank you towards the future. Ok. This is confusing. If the Fiends have the power to get Garland back to the past, why didn't they already send theirselfves into the future. Maybe they are only able to get things to the past. But it still leaves some open questions. Like why did Garland send the Fiends to the future? To destroy your party or to destroy the world?
Why have the Fiends arrived in different times?
And more questions, so help me out to get the plot