In this excellent book Mr. D'Este delves deep into the near bitter warfare raged amongst the Allied high commands as they planned and prepared for Operation Husky: the invasion of Sicily.
The differences of opinion regarding high strategy and the tactical details between the Americans and the British helped to create a still lasting aura of mistrust between the Allies that would follow them throughout the course of the war. The eventual success of the invasion, flawed though it was, did nothing to distill the lingering feelings of mistrust between the Allies, and in fact only served to heighten them when the invasion of mainland Italy turned into a fruitless bloodbath against outnumbered, but brilliantly led, German forces.
As far as the battle itself D'Este shows the utter ineffectiveness of the Italian armed forces to defend their own soil. This can be explained by the fact that not only did Italy never have its heart in the Second World War (as they did in the First, though that was a bit of a disastrous bloodbath so it explains why they were not remotely grateful for a second go), but they resented the successes and maltreatment of their erstwhile allies the Germans. The Germans never accepted the Italians as a full fledged ally militarily, much like the Germans viewed the Austro-Hungarians in WWI as a corpse they were shackled to, the Germans were always grumbling about having to save Italian chestnuts from numerous fires. Thanks to low morale, inept leadership, poor equipment, meager rations and deplorable medical care, and uncaring 'allies' the Italians essentially folded within the first few days and never again participated on the Axis side of WWII.
The Americans and British never could see eye to eye on operational objectives. Montgomery created a hell of a row between the allies when he suggested, from a position of common sense, a unified command structure for the battle. This would have put the British in overall command, sure to infuriate Americans who already felt slighted by their British cousins and felt they still had something to prove after their initial thrashings at the hands of the Germans in the first battles in Tunisia. So when Patton swung his 7th Army westwards, to hook around behind the main German defensive lines around Mt. Etna, seize the strategically important port of Palermo, and then arrive behind the Germans and cutoff their retreat at Messina, he left the British to slug it out with well equipped, well dug in German defenders who were worlds ahead in terms of effectiveness compared to the Italians.
When Patton took Messina ahead of Montgomery, though he too had to fight some very tough, bloody battles the closer he got to Messina, especially Troina, he had won the 'race' to Messina but had almost lost the campaign. And, in a way, the Allies did lose the larger campaign.
The main story of the Sicilian Campaign, at least to my eyes, is not the overall Allied material triumph, or the Italian collapse that followed, but the outstanding performance of a small cadre of German divisions that took everything the Allies could dish out, and returned the favor time and time again.
The Germans, knowing that they could easily be trapped and either annihilated between the pincers of the 7th US and 8th British Army or forced to surrender, subsequently waged a truly brilliant defensive campaign that maximized Allied casualties and bought them the time for a relatively junior officer to keep open the Messina Straits where the Germans then not only removed all but their dead and seriously wounded and previously captured to the mainland, but their heavy equipment too. That was the true feat of arms of the Sicilian Campaign: the amazing performance of the badly outnumbered Wehrmacht. A terrible harbinger of things to come in Italy.
All in all an excellent read, my only quibble would be the lack of in depth study at the Axis plans for defense and an inside look at German headquarters as the Allies waged their war of conquest on Sicily. Still this is an excellent book, easily the best on the Sicily Campaign.