Space industrialization will produce new and less expensive space transportation systems.
Space industrialization will produce radically new materials that will have military implications in terms of increased strength, decreased weight, and various other physical properties.
Some may grow large enough to absorb other branches of the military, others may be reabsorbed into other branches.
In William Keith's Galactic Marines series one of the themes of the early novels is how the US Marines fight being absorbed or eliminated.
Protection of space property is very dependent upon the basic military rationales, doctrines, and operational realities of cis-lunar celestial mechanics.