Moroni quoted from Joel (second chapter, from the 28th verse to the last) and said that the prophecies would shortly be fulfilled. (JS history 1:41)
The book of Joel = major source of information on the battle of Armageddon.
Zion (the righteous people of Enoch, not the buildings) was taken up to heaven and "shall return during the Millenium, when the Lord brings again Zion; and its inhabitants shall join with the New Jerusalem which shall then be established."
"the place of Zion, or the land of Zion, "is North and South America". (prophet J. Smith)
Joel 2: 2-11
An event of the latter days known as the battle of Armageddon is described in these verses. Like the locusts that devour the crops and cover the heavens with blackness because of their numbers, so "a great people and a strong" shall descend upon the land of Israel in the latter days. (compare to Rev. 9:1-10 & Ezekiel 38: 8-9) So great shall be the number of this people that "the earth shall quake before them". The sun, moon, and stars will be darkened.
Horses = war
Chariots = a powerful army
Elder Joseph Fielding Smith: "Here we have a great, terrible army, marching with unbroken ranks and crushing everything before it, finding the garden like Eden before them, leaving the wilderness behind, causing mourning, causing suffering; and so the prophet raises the warning voice, and that voice is to us, if you please, that we might turn unto the Lord and rend our hearts."
When these events occur they will strike fear into the hearts of Jerusalem's inhabitants. The siege against the city will be very severe. The relentless army will overrun the land of Israel. The city walls will be breached and the houses plundered. The phrase "when they fall upon the sword, they shall not be wounded" may simply be a way of saying that the armaments used against the invaders will be ineffectual.
One major theme of the Old Testament prophets is that although there will be a great apostasy in Israel, in the end Israel will be restored to the covenant (the gospel) and become faithful.
The last days are to be characterized by the pouring out of the spirit upon all flesh... That spirit is not only the Holy Ghost but also the Spirit of Christ, that spirit which enlightens every one. Sons and daughters will prophesy - preach, exhort, pray, and instruct so as to benefit the Church. Direct revelation will be given. Young men and women who are representatives of the Lord will be inspired. The gifts of teaching and inspiration will be given to all classes and levels of people. The Lord will call and qualify those he chooses. He will pour out his spirit upon them, and they will be endowed with the gifts necessary to convert sinners and to build up the Church.
Israel, who had been scattered among the nations, will receive a change in her fortunes, and retribution will come upon her enemies in the Valley of Jehoshaphat, literally, the 'Valley of Decision' in Hebrew. Just where this valley is located is not entirely clear. Most likely it is the Kidron, a narrow valley between Jerusalem and the Mount of Olives. This passage seems to refer to the final scenes of the battle of Armageddon in Jerusalem, when the great earthquake will strike the massive army and Jesus will appear on the Mount of Olives to deliver Israel.
...The Lord will be the strength fo Israel and will smite her enemies... And then Judah will know that Christ is the Lord their God, for he will stand onthe Mount of Olives, which will cleave in twain and Judah will see him as their delivering Messiah. They will ask about his wounds and learn that he is the Christ, and their mourning will know no bounds, for they will know that this is he for whom they have waited and whom their fathers crucified.
Jerusalem will be pure = no impure people will be permitted to enter or pass through the city.
Because Moroni quoted a part of the book of Joel to Joseph Smith and said it was "not yet fulfilled, but was soon to be", we should carefully study the message and learn of the things we need to do before the great and terrible day of the Lord.
(see Old Testament Study Guide, p. 83 - 86)