WWI, The Great War, promoted adding of unarmed combat to military combat training curriculum of all major militaries, which ware mostly concerned with bayonet fencing till this time. This was time that saw birth of term hand-to-hand combat (or H2H).
The most advanced become British military hand-to-hand combat system that has been used by Americans and greatly influenced Continental Europe.
Russian development was late as mid 30th and mostly based on Vasili Oshchepkov Judo and its derivations.
WWII saw birth of modern Special Operation Forces. Hand-to-hand combat training was seen always as key element of their mission preparation.
Post-war period was anything but peaceful. Israel Independence Wars saw formation of Krav Maga based on British experience with influx of a variety of techniques from all known systems filtered by their simplicity and effectiveness.
Nowadays military is evolving more toward Special Forces and military combat training changing along with it.
Types of combat by application