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.
Secondary Sources. The most common type of source you are likely to encounter is a secondary source. A secondary source is any source about an event, period, or issue in history that was produced after that event, period or issue has passed. Aside from a textbook, the most commonly assigned secondary source is a scholarly monograph - a volume on a specific subject in the past, written by an expert. Also common are articles in scholarly journals, which are similar to monographs, but on a smaller, more focused scale.