I believe this refers to the Romans in 70 AD.
And when you examine the order of things in this prophecy compared to Matthew's prophecy, you will see, Bear with me on the quotes, just follow the parts I bold and color
Luke 21:7-27 KJV
7) And they asked him, saying, Master, but when shall these things be? and what sign will there be when these things shall come to pass?
8) And he said, Take heed that ye be not deceived: for many shall come in my name, saying, I am Christ; and the time draweth near: go ye not therefore after them.
9) But when ye shall hear of wars and commotions, be not terrified: for these things must first come to pass; but the end is not by and by.
10) Then said he unto them, Nation shall rise against nation, and kingdom against kingdom:
11) And great earthquakes shall be in divers places, and famines, and pestilences; and fearful sights and great signs shall there be from heaven.
12) But before all these, they shall lay their hands on you, and persecute you, delivering you up to the synagogues, and into prisons, being brought before kings and rulers for my name's sake.
13) And it shall turn to you for a testimony.
14) Settle it therefore in your hearts, not to meditate before what ye shall answer:
15) For I will give you a mouth and wisdom, which all your adversaries shall not be able to gainsay nor resist.
16) And ye shall be betrayed both by parents, and brethren, and kinsfolks, and friends; and some of you shall they cause to be put to death.
17) And ye shall be hated of all men for my name's sake.
18) But there shall not an hair of your head perish.
19) In your patience possess ye your souls.
20) And when ye shall see Jerusalem compassed with armies, then know that the desolation thereof is nigh.
21) Then let them which are in Judaea flee to the mountains; and let them which are in the midst of it depart out; and let not them that are in the countries enter thereinto.
22) For these be the days of vengeance, that all things which are written may be fulfilled.
23) But woe unto them that are with child, and to them that give suck, in those days! for there shall be great distress in the land, and wrath upon this people.
24) And they shall fall by the edge of the sword, and shall be led away captive into all nations: and Jerusalem shall be trodden down of the Gentiles, until the times of the Gentiles be fulfilled.
25) And there shall be signs in the sun, and in the moon, and in the stars; and upon the earth distress of nations, with perplexity; the sea and the waves roaring;
26) Men's hearts failing them for fear, and for looking after those things which are coming on the earth: for the powers of heaven shall be shaken.
27) And then shall they see the Son of man coming in a cloud with power and great glory.
First Jesus gives much the same introduction to the signs of the end as in Matthew, but here He says, "but before all these", and goes on to prophecy persecutions and so forth, culminating in the surrounding of Jerusalem by armies, leading to the captivity of Israel into all nations. Then He returns to His prophecy of His coming in power and glory.
In Matthew,
Matthew 24:4-16 KJV
4) And Jesus answered and said unto them, Take heed that no man deceive you.
5) For many shall come in my name, saying, I am Christ; and shall deceive many.
6) And ye shall hear of wars and rumours of wars: see that ye be not troubled: for all these things must come to pass, but the end is not yet.
7) For nation shall rise against nation, and kingdom against kingdom: and there shall be famines, and pestilences, and earthquakes, in divers places.
8) All these are the beginning of sorrows.
9) Then shall they deliver you up to be afflicted, and shall kill you: and ye shall be hated of all nations for my name's sake.
10) And then shall many be offended, and shall betray one another, and shall hate one another.
11) And many false prophets shall rise, and shall deceive many.
12) And because iniquity shall abound, the love of many shall wax cold.
13) But he that shall endure unto the end, the same shall be saved.
14) And this gospel of the kingdom shall be preached in all the world for a witness unto all nations; and then shall the end come.
15) When ye therefore shall see the abomination of desolation, spoken of by Daniel the prophet, stand in the holy place, (whoso readeth, let him understand:)
16) Then let them which be in Judaea flee into the mountains:
Jesus continues in a single prophetic narrative without that same sort of paranthetical, "but before all this", as He goes on to prophesy the Abomination of Desolation and subsequent great tribulation, affecting all life on the planet. "No flesh would survive."
Much love!