Hi Sir Ahwatukee,
The Day of the Lord Isaiah is describing is the Medes smashing up Babylon.
First of all, there is nothing in the scripture that would tie in "the Medes smashing up Babylon." And it does not fit the criteria of destroying the inhabitants of the earth. And second, this is why I drew your attention to the v.9 & 10 showing that the day of the Lord as being a future event by comparing the prophecy of the darkening of the sun and moon with Matthew 24:29. It puts 'The Day of the Lord' which Isaiah is referring to as being future. Below are the scriptures in question:
====================================
Wail, for
the Day of the LORD is near;
it will come as destruction from the Almighty.
7Therefore all hands will fall limp,
and every man’s heart will melt.
8Terror, pain, and anguish will seize them;
they will writhe like a woman in labor.
They will look at one another,
their faces aflame.
9Behold,
the Day of the LORD is coming—
cruel, with fury and burning anger—
to make the earth a desolation
and to destroy the sinners within it.
10For the stars of heaven and their constellations
will not give their light.
The rising sun will be darkened,
and the moon will not give its light.
=======================================
Compare with Matthew 24:29 where the darkening of the sun and moon are the sign of the Lord's immediate return, which hasn't happened yet.
Immediately after the tribulation of those days:
‘
The sun will be darkened,
and the moon will not give its light;
the stars will fall from the sky,
and the powers of the heavens will be shaken
=======================================
Both Isaiah and Matthew are speaking about the same event, which is the 'The Day of the Lord' which is yet future and which the majority of the book of Revelation is giving in detail. Zephaniah, as well as other prophets, prophesy regarding 'The Day of the Lord.'
The great Day of the LORD is near—near and coming quickly.
Listen, the Day of the LORD!
Then the cry of the mighty will be bitter.
15That day will be
a day of wrath, a day of trouble and distress,
a day of destruction and desolation, a day of darkness and gloom,
a day of clouds and blackness,
16a day of horn blast and battle cry
against the fortified cities, and against the high corner towers.
17I will bring such distress
on mankind that they will walk like the blind,
because they have sinned against the LORD.
Their blood will be poured out like dust and their flesh like dung.
18Neither their silver nor their gold will be able to deliver them
on the Day of the LORD’s wrath.
The whole earth will be consumed by the fire of His jealousy.”
For indeed,
He will make a sudden end of all who dwell on the earth.
==================================================================
The Day of the Lord is a future event which will begin after the church has been gathered.
The reference to bringing distress on mankind and making a sudden end of all who dwell upon the earth, will be carried out via the seals, trumpets and bowl judgment, as well as the plagues that the two witnesses will bring.
A study of everywhere that 'The Day of the Lord' is prophesied would be helpful in understanding this as a future event leading up to the end of the age.