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.
Americans use many types of energy. Petroleum, natural gas, coal, renewable energy, and nuclear electric power are primary sources of energy. Electricity is a secondary energy source that is generated from primary sources of energy.