There are three common threads in Revival History:

Some kind of crisis

Unction on the church to pray

A heart to repent  -- 1st in the church, 2nd in the world at large

The Holy Spirit plays a specific role in this process, as Jesus described in John 16:8-11

John 16:8-11 8 When he comes, he will convict the world of guilt in regard to sin and righteousness and judgment: 9 in regard to sin, because men do not believe in me; 10 in regard to righteousness, because I am going to the Father, where you can see me no longer; 11 and in regard to judgment, because the prince of this world now stands condemned.