In ancient Scotland, where Shakespeare has set the play Macbeth, Lady Macbeth was prohibited from gaining power herself, since power was recognized first based upon how good a warrior a man was. Women did not fight in battles, so they had no way to win political respect or position. So, Lady Macbeth, if you are following Shakespeare's plot, is supporting and encouraging (pushing?) her husband towards the ultimate power. She wants him to murder the king so that he can fulfill a prophecy and become king himself.
In a modern sense, this would translate to a world where a man's ability to display his "warrior-like" qualities would be important. Some ideas would be:
- a politically unstable country, one that might be ruled by the military
- the Mafia
- the world of gangs
- a cartel of drug lords
Each of these would be the sort of dog-eat-dog environment suitable for the situation that unfolds in Macbeth and that allows him to murder the leader and gain power. They also suggest worlds in which it is "might" rather than "right" that carries the day, an environment that would suit the circumstances of Macbeth.
I have assumed here that you need to stick to the plot as it is given in the play, even though you are creating a modern version of the play. There are at least two great "modern" examples of Macbeth, one an Australian version of the Shakespeare text, made in 2006 by Geoffrey Wright and an older Japanese film based on this play by Akira Kurosawa called Throne of Blood. Both should give you some ideas for updating the events and themes of Shakespeare's play.
For more on the films I mention above, and on making modern connections, please follow the links below.