Before WWI, strategically, machine guns were offensive weapons. They were used to expand the European empires against opponents who didn’t have them.
Come WWI, it turned out that they were defensive weapons which made offensive operations very hard if both sides had them.
Armor and air made fast offensive operations possible in WWII, and aircraft carriers made air the queen of the ocean and the king of force projection against nations without large air forces.
Over the past twenty years two major things have changed in military technology. I’ve written about both in the past.