[central_va]

The USA is basically an island nation, a huge one but with no real land threat. A serious argument could be made that the USA doesn’t need much of an Army at all. All defense spending should be on the Navy and the Marines. The Navy could take over the Air Forces functions also.

[BroJoeK]

central_va: "A serious argument could be made that the USA doesn't need much of an Army at all."

And indeed, that was exactly US strategy in the years before, say, 1940.
Presidents like the two Roosevelts loved the Navy, and did what they could to support it, even at the expense of Army men & equipment.
One result was that while the Navy was fighting & winning great battles in 1942, the Army was still struggling to figure itself out well into 1943.

My Dad's WWII division, for example, spent years in training for Pacific beach landings before their trials by fire in 1944 & '45.
As a result, Army strength has been maintained at much higher levels... until quite recently.
Still, Army and Air Force combined are budgeted double that of Navy & Marines, perhaps reflecting requirements of the War on Terror.
However, I also note that of the top 15 military development programs listed here, only one relates directly to the Army.

Historical military spending to gdp (lower blue line), since Korea:
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