Weapons technology

Modern offensive and defensive armament is spectacularly advanced by 20th-century standards.

The development of fusion reactors and high-efficiency storage makes energy limitations practically moot, and developments in computer technology and EM physics have made forcefields, EMP shielding, highly versatile and sensitive sensor systems, various kinds of energy-beam weaponry, advanced robotics (and even AI), and all kinds of other technology ubiquitous within military organizations and only slightly less so (though frequently illegal) outside of them.

Even that pales in comparison to the advances made in biotechnology.

No full-scale war has been fought on Earth for some time now, and it is genuinely unclear -- even among optimists -- what the outcome of fighting one with modern weapons would be.