Paul wrote 2 Thess 2 because some people had drawn the conclusion we were already in the tribulation period.  He said,

"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. " (2 Thess 2:1)

He is not likely to have said this unless someone had tried.  And why would they believe it?

Paul wrote during a period in which Christians were frequently being put to death by the government.  What they understood about the end times was that Christians will be martyred frequently at the hands of the government when the False Messiah rises to power.  They were being martyred frequently at the hands of the government.  So it was not a big leap to conclude that Caesar was the False Messiah at the time.  That was a wrong conclusion, but it was a conclusion many Christians came to simply because Christians were being put to death by the Government left and right.

So Paul found it necessary to explain to them what would be different between their present times and the End Times.  So he decided to enumerate several events;

• The Apostacy
• The "man of sin"
  • exalting himself above all gods
  • claiming to be god
  • sitting in the temple
  • would perform many miracles

There was no great apostacy.  In fact revival was spreading throughout the Roman Empire.  And no Caesar ever did all of those things.  Most Caesars were worshipped as gods AFTER their death, but not before.  And none performed miracles or drew worship while still alive.

Paul was writing before the book of Revelation.  but thanks to it, we can gleam other signs such as

• The abomination of desolation, which some Early Christian writers (including Iranaeus, Justin, Augustine and Chrysostrum ) claim is what Paul meant by "Apostacy".  I documented that at http://www.fivedoves.com/letters/may2015/jovial53-2.htm .
• the mark of the beast on the right hand or forehead
• the 2 witnesses
• the many plagues, etc.

Shalom,

Joe