The Italian campaign ran for less than a year before it was eclipsed by D Day and fighting in NW Europe as the decisive ground campaign by the western allies. Italy was always regarded as a peripheral campaign, and kind of a supporting attack which would draw German forces away from the main efforts in NW Europe and the Eastern Front.
Unfortunately the geography of Italy makes it a defenders paradise where small forces can obstruct and delay much larger forces. At the end of the day it was a question of just who was being diverted in Italy, the Germans or the Allies. The terrain never changes; as Hannibal demonstrated the best way to enter the Italian "boot" is from the top rather than from the toe.
The US also had considerable numbers of forces engaged in Italy, but the military and public focus shifted to NW Europe after D Day. Forces were skimmed away from Italy as the campaign in NW Europe progressed incl 1 Cdn Corps which was relocated in early 1945. There is a lot of reference material on the Italian campaign, but its just not as popular as the main effort in France and Germany. That doesn't diminish the efforts of the troops in Italy one iota, but its tough to find people who have visited the Cdn battlefields in Italy to the same extent as in France, Germany and Holland.
The Germans knew all along they'd be retreating, battle plan was to make it as difficult and expensive as possible.
Grizz