US Broad Front Doctrine

What was the doctrinal thinking behind the US Preference for continuous assaults on a broad front?

One of the big differences between US and British (and German) Doctrine was that the US Army have did not appear to have the same emphasis on concentration of effort at a single point.

One of the fundamental principles of the German way of war was for the commander to determine the point of mainn effort -the Schwehrpunkt.

The British under Montgomery famously developed tactics based on set-piece battles; Colossal Cracks (Stephen Hart). This firepower-based approach concentrated on a relatively narrow sector, capturing important ground prepared for the inevitable counter attack. Each operation was meticulously prepared with the intention of minimising casualties. There has been much criticism of this approach since Hart's 2004 (?) book. (I am not directly interested in any more detailed criticisms of Monty's methods. I have tons of them)

British commentators have criticised the US approach in Italy and Normandy for attacks over a wide frontage. (1st Cassino January 1944, Battle of the Hedgerows June/July 1944)

What was the logic behind the US Commanders' thinking, "Hey, I'll spread my troops along the line and order everyone to attack until the enemy breaks."

Can anyone recommend any primary sources for this US doctrine?
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