The tet wants earth’s resources
The Tet , probably an alien civilization, wants to get earth’s resources and specifically water. After the Tet destroyed earth’s moon they created drones that can do the resource collection process.
The original jack died
The original jack died in the events before the movie began. He was killed by the Tet.
Jack and Victoria were cloned
The Original Jack was killed by the Tet in pre-movie events. Jack and Victoria were cloned by the Tet after they were killed. Jack’s clone starring the movie is given the number 49.
Jack’s memories were wiped out
After the cloning operation the original memory of the person is wiped out. However people have the capacity to remember the lives of their original versions and this explains the flashbacks jack used to get. (See The Illusionist (2006) Movie Explained)
The Scavs are human resistance
The Scavs are not Aliens but they are the remaining human resistance fighting the Tet. Jack was led to believe that the Scavs were evil beings until he discovered later that they were humans.
The drones are there to kill humans
One of the main functions of the drones is to kill the surviving humans. The Alien civilization wanted to make sure that no human survivors remain. (See Sam Was Here (Nemesis) 2016 Movie Explained)
Jack 49 finds jack 52
Jack 49 accidentally came across Jack 52 which is another clone for the original Jack made by the Tet.
Julia is pregnant with Jack 49’s baby
Julia, Jack’s original wife, got pregnant by Jack 49. Julia gave birth to Jack 49’s baby.
Jack 49 destroys the tet and dies
Jack 49 sacrificed himself to blow up the Tet so that he can save earth.
Jack 52 replaces jack 49
Jack 52 found Julia and was able to replace jack 49 for he looked the same and had his same memories.
Oblivion (2013) Movie Explained
Oblivion Movie Review & Film Summary (2013) | So, What Exactly Is Happening in Oblivion (2013)?