If Abraham Lincoln were to write a letter it would be considered a primary source because of Lincoln having been there to experience and be apart of it. Whereas an article by a journalist describing what happened during the time the letter was being written would be a secondary source for the journalist wasn't there.
The United States Decleration of Independence is the pronouncement adopted by the Second Continential Congress meeting at the Pennsylvania State House in Philadelphia.
The German economy was very weak and needed a strong leader to unite them all under one cause. Another reason is they were angry that Germany had lost WW1