The Treaty of Versailles in the mind of the Germans stabbed them in the back, especially the guilt clause that made them take blame for the First World War. Hitler capaitalized on these sentiments and used them to rally the German people.
Primary sources are the first hand evidence left behind by participants or observers at the time of events. Primary sources originate in the time period that historians are studying. They vary a great deal.
3. Secondary sources. The function of these is to interpret primary sources, and so can be described as at least one step removed from the event or phenomenon under review. Secondary source materials, then, interpret, assign value to, conjecture upon, and draw conclusions about the events reported in primary sources.