Prior to WW One, the USMC was very small, basically serving as guards on ships and at embassies, rarely in the news. Then the Marines assembled two infantry brigades that served as part of the 2nd Army infantry division and got noticed, first at Belleau Wood, most Americans had never heard of them previously.
The first Marine Division was not constituted until 1940, then six were assembled in WW 2, all in the Pacific, in contrast with nearly 100 Army divisions.
The Russians had over 300 army divisions in WW2, but they were smaller, and with less logistical tail.