Mmmmm … ham.
I bloused my pants into my boots when working. If I ws in the field to look at something and was headed to somewhere nice after I would blouse my pants.
With my pants over my boot tops they would keep chaft, dirt or slag and other stuff ut of my boots.
They tuck their jeans in their boots so that the sheep’s hind legs can fit in there too. 
The Army blouses their boots to this day. The thing with the paratroopers is that they wear jump boots and blouse them in their Class A uniform as well, not just fatigues.
Cool. We had a bunch of jump qualified folks from both USAF & USA, but I never saw any Army folks in Class A’s. We were generally out in the field.
I imagine the guys in the Motley Crue tribute band I’m seeing next Sunday will tuck their jeans into their cowboy boots, mainly because they’ll be too tight to go over them.