No doubt the spiritual kingdom is now, but the preceding verses are taken by most people to be the 7 year tribulation which would indicate the Op verse refers to the Son of mans return at the time of the tribulation.
2Th 2:1 Now we beseech you, brethren, by the coming of our Lord Jesus Christ, and by our gathering together unto him,
2Th 2:2 That ye be not soon shaken in mind, or be troubled, neither by spirit, nor by word, nor by letter as from us, as that the day of Christ is at hand.
2Th 2:3 Let no man deceive you by any means: for that day shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition;
2Th 2:4 Who opposeth and exalteth himself above all that is called God, or that is worshipped; so that he as God sitteth in the temple of God, shewing himself that he is God.
When there is a falling away first, which is the condition of the world in response to the Gospel, which they stop the preaching of it worldwide, for religion is about evolution, and people can still evolve, and anything contrary is a hate crime, and disturbing peace that they want, which happens during the first three and one half years, which is the time the world will not want to hear the truth of the Bible, but according to their own lusts, and the man of sin, New Age Christ claims to be God, and they follow him and take the mark of the beast, which has to do with technology, then the saints can be gathered unto Christ.
The beast persecutes the saints for the last three and one half years, for they make war with the saints and prevail against them, and they are given in to his hands for three and one half years, and when he shall have accomplished to scatter the power of the holy people all things shall be finished, which then comes the end when the Son shall deliver up the kingdom to the Father when He shall have put down all rule, and authority, and power.
Zec 14:1 Behold, the day of the LORD cometh, and thy spoil shall be divided in the midst of thee.
Zec 14:2 For I will gather all nations against Jerusalem to battle; and the city shall be taken, and the houses rifled, and the women ravished; and half of the city shall go forth into captivity, and the residue of the people shall not be cut off from the city.
Zec 14:3 Then shall the LORD go forth, and fight against those nations, as when he fought in the day of battle.
Zec 14:4 And his feet shall stand in that day upon the mount of Olives, which is before Jerusalem on the east, and the mount of Olives shall cleave in the midst thereof toward the east and toward the west, and there shall be a very great valley; and half of the mountain shall remove toward the north, and half of it toward the south.
Act 1:9 And when he had spoken these things, while they beheld, he was taken up; and a cloud received him out of their sight.
Act 1:10 And while they looked stedfastly toward heaven as he went up, behold, two men stood by them in white apparel;
Act 1:11 Which also said, Ye men of Galilee, why stand ye gazing up into heaven? this same Jesus, which is taken up from you into heaven, shall so come in like manner as ye have seen him go into heaven.
Act 1:12 Then returned they unto Jerusalem from the mount called Olivet, which is from Jerusalem a sabbath day's journey.
Zec 14:5 And ye shall flee to the valley of the mountains; for the valley of the mountains shall reach unto Azal: yea, ye shall flee, like as ye fled from before the earthquake in the days of Uzziah king of Judah: and the LORD my God shall come, and all the saints with thee.
Rev 19:11 And I saw heaven opened, and behold a white horse; and he that sat upon him was called Faithful and True, and in righteousness he doth judge and make war.
Rev 19:12 His eyes were as a flame of fire, and on his head were many crowns; and he had a name written, that no man knew, but he himself.
Rev 19:13 And he was clothed with a vesture dipped in blood: and his name is called The Word of God.
Rev 19:14 And the armies which were in heaven followed him upon white horses, clothed in fine linen, white and clean.
Rev 19:15 And out of his mouth goeth a sharp sword, that with it he should smite the nations: and he shall rule them with a rod of iron: and he treadeth the winepress of the fierceness and wrath of Almighty God.
Zec 14:9 And the LORD shall be king over all the earth: in that day shall there be one LORD, and his name one.
Isa 11:9 They shall not hurt nor destroy in all my holy mountain: for the earth shall be full of the knowledge of the LORD, as the waters cover the sea.
After the beast makes war against the saints they shall be resurrected to heaven, and the world will attack Israel and then Jesus will come back with the saints and defeat the world, and save Israel, and the kingdom restored to Israel, and Jesus and the saints will rule over the heathen that God spared at the battle of Armageddon, so there is a physical reign of Christ on earth.
Jesus has to fulfill the law, which has to be done on earth, which He has not fulfilled the role of perfect King on earth, for He came as a humble servant to save us, and not to rule, so there has to be a time of Jesus ruling on earth that people can actually see Him.
Zec 12:1 The burden of the word of the LORD for Israel, saith the LORD, which stretcheth forth the heavens, and layeth the foundation of the earth, and formeth the spirit of man within him.
Zec 12:2 Behold, I will make Jerusalem a cup of trembling unto all the people round about, when they shall be in the siege both against Judah and against Jerusalem.
Zec 12:3 And in that day will I make Jerusalem a burdensome stone for all people: all that burden themselves with it shall be cut in pieces, though all the people of the earth be gathered together against it.
Some people will say that Zechariah 14 is when the Roman Empire went against Jerusalem, the Jews, but that is not true for it says that God will gather all the nations together against Jerusalem.
But then some will say but it means the then known world, bu that is not true for the Roman Empire went against them, for was Egypt and Africa there that was known, and was Asia there that was known, and was Arab nations there that was known, they were not but it was the Roman Empire that went against them, and not even all nations in the then known world.
The whole earth shall be gathered together against Jerusalem.
The first attack God allowed it to happen without fighting against the Roman Empire, but the second attack on Jerusalem God fights them and puts them down which is in the future, which then the LORD is King over all the earth, and there shall be one LORD, and His name one, and the knowledge of the LORD shall cover the whole earth, which all people of the world will only acknowledge the God of Israel and no one else from that time forward, which we know could not be true back then.