IMO - THE GREAT TRIBULATION:
Occurs when Religion is attacked. It appears to be a destructive power apart from God but without His intervention 'no flesh would be saved' on earth (Matthew 24: 21 and 22).
A close friend from many years ago once said when religion is attacked it will not go away quietly but be a very bloody, very violent event. I believe he is right.
As we know, the zealots of religion are capable of anything since they believe they have God's favor. If they have Biological Weapons they will use them, if they get Nukes...they will use them. Add to that the power of Satan and his demonic army warring against ALL humanity in an attempt to thwart God's will for His faithful followers and His earth.
In recent years we have seen new diseases popping up around the globe, many potentialy VERY DEADLY. Violent weather around the world is something common now that wasn't in the not-to-distant past.
I do believe the present Ruler of this world, Satan is preparing for God's War in a way that will prove most harmful to humanity. I also am not convinced that everyone who dies during the GT will not be resurrected, but everyone who dies 'during Armageddon' definately will not.
IMO - ARMAGEDDON:
Is what Jehovah uses to end the Great Tribulation. I suspect Armageddon will be a prolonged event like the flood of Noah's day which took 40 days and nights to complete.