"The second is the obsolescence of heavy armor in general. The US is literally only a few years away from deploying light, compact, rapid-fire weapon systems that can defeat all existing and projected future armor systems and with more range than any tank gun."
The Third reason in the future will be remote-controlled unmanned battle tanks; the Fourth will be fully automated robotic tanks a generation after the remote-controlled unmanned tanks.
Still, the M1 will be around for a while, as having a well-trained, disciplined, motivated human inside an Abrams continues to have enormous military advantages. In fact, it may well turn out that it is the Air Force that makes the remote-controlled unmanned transition first, followed only much later by the Army. Boots on the ground and grunts in the tanks may simply be more difficult to obsolete than jet-fighters that already fire robotic missiles.
Boots on the ground and grunts in the tanks may simply be more difficult to obsolete than jet-fighters that already fire robotic missiles. Yup. They won't be replacing humans on the ground for some time, at least for some tasks. Driving and repairing vehicles in the field, for example, is still something DARPA has not been able to solve without a human in the loop, whereas moving the Air Force to almost purely robotic vehicles is being aggressively road mapped because there is little stopping this conversion technologically. The groundpounder's job is safe for the time being, though they will be doing less and less of the actual fighting.