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.
In scholarly writing, the objective of classifying sources is to determine the independence and reliability of sources. Though the terms primary source and secondary source originated in historiography as a way to trace the history of historical ideas, they have been applied to many other fields.