Thank you.....This is a prophecy of the "Day of the Lord" the Day of the Lord is considered not just one day but many days in which the Lord God Jehovah will judge the people, His enemies (unbelievers), deliver His people (Israel) to the land that He gave them and bring about the Millennium (1000 years of physical rule by Jesus Christ ).
Thus, in 1 Thes 5, Paul is speaking to believers in the Thessalonian church. He was speaking/prophecising about the time when the scripture of Rev 4 through 19 tells us the events that will happen to the dwellers of the earth.
My point, many are always trying to make phrases, words, etc. say things that God has not said. As 1 Thes 5:3 states, a false piece will be followed by a sudden destruction. In Rev 6, the judgements of the Scrolls, War War III comes upon mankind, Yes, it is a judgement of God and during this time period, more than 1.875 billion people will die. Is that sudden enough for Jesus tells us in Mat 24:22.."And except those days should be shortened, there should no flesh be saved: but for the elect's sake those days shall be shortened." Yes, this seems to be a nuclear war between nations and kingdoms. Further down the road of time, the Trumpet Judgements will kill another 1/3 of the remaining population or another 1.873 billion people. This is based on the present population of 7.5 billion people worldwide. I doubt that it gets any small by the time the "Day of the Lord " gets here. These are told to us in no uncertain words, not symbols, not allegories,etc. just plain literal words of GOD.