Prior to WWI, the Marines NEVER fought above the level of Company EXCEPT on rare occasions (and on those occasions commandeered by Army Officers, for no Marine Officers had any experience commanding units above Company level, thus when Five Marines Companies were sent to Harper's Ferry in 1859 they were under the command of JEB Stuart. The Marines biggest operation during the Civil War was Ft. Fisher, where it was a diversionary attack for the larger Army Attack. In fact the Marines backed up the Sailors who were in the first line of attack (at least the Marines had Rifles, the sailors were given pistols and cutlasses, both Marines and Sailors were massacred).
During WWI for the first time Marines were organized at Battalion level and Brigade level, but the Army was using the "Square Division" of Two infantry Brigades of Two Infantry Regiments with each division having 3 Infantry Battalions (and each Battalion having Three Companies, with four Artillery regiments, engineer, Medical and other support units to add up to 25,000 men per Division). The Marines thought they were having TWO Brigades was the largest they had ever been, but the Army could no figure out how to use them, No Division Support units (i,e, Artillery, engineering, Medical, Transportation and other units). The Marines were merged with a National Guard Division that needed an additional Infantry Brigades (The unit had the Support units to supply the Division but needed an additional Infantry Brigade).
After WWI the Marines started to developed Artillery and support units and during WWII finally formed into Divisions (Triangular Divisions of Three Regiments per Division, each Regiment having Three Battalions of Three Companies, with Support troops about 15,000 men, this reflected the Armies adoption of the triangular Division in 1940 and implementation between 1940 and 1942).
The US Army had used Divisions and Corp (Generally three division to to a Corp) during the Civil War, but reverted to just having Regiments at the end of the War. Divisions and Corp were reformed during the Spanish-American War, WWI and in 1939. Except for those time periods even the Regular Army did NOT have Divisional size units.
Now the National Guard did retain Divisional formation after the Civil War, thus the 28th Division is the oldest Division in the US Army, for it was the Pennsylvania National Guard unit, and Pennsylvania kept its National Guard Regiments formed into a Division after the Civil War and till this day (Other states did the same).
My point is simple, the Marines were used when nothing bigger was available. The Navy was the point, the Marines were used if a small force was needed (company size or less, i.e. 100 men) if more men were needed the Army was used (For Example the Philippines and Cuba during the Spanish Civil War). If you needed Divisional size units the National Guard was called up more for the people who had senior personnel who had experience in moving large number of troops. Thus in 1917, the US army was not readily to fight till 1918. In 1939, a Divisional size unit was tested out in Maneuvers. The Army actually had a plan to raised 267 Divisions during WWII, but then the Navy told them they only could Transport 100 divisions. For this reason the Army Raised 90 Divisions for WWII and the Marines were permitted to have ten divisions (Do to smaller support requirements i.e. no Corp level Troops needed for the Marines, through all Army divisions were formed into Corps, Armies, and then Army Groups).
The Marines were noted by their absence in Europe during WWII (The Navy wanted them in the Pacific and the Navy provided the Corp, Army and Army Group support functions). The Marines did serve in Europe during WWI, Korea and Vietnam, but not as the spear of the military NOT just a part of the Military, like the Army, Navy, Air force and Coast Guard (I have to mention the Coast Guard, during WWII during Guadalcanal and Marines were able to get out of a mess by Covering Fire supplied by a Coast Guard Cutter). All the Services have a function, together they provide a defense to this nation, as a whole not each by themselves.
http://en.wikipedia.org/wiki/Fort_Fisher