Which time?
Let's take one time, the Declaration of War against the United States in 1941, which Germany claimed it did, because it felt that the US was no longer neutral in the conflict and was supporting the opposited side (Great Britain) as well as fighting against its ally (Japan).
<span />
Between 1946 and 1954, the House Committee of Un-American Activities and Senator Joseph McCarthy attracted public attention by investigating 1. allegations of communist influences in government. HUAC, as the committee was called, investigate claims of communist ties not only in the government, but in other industries as well such as the filmmaking industry in Hollywood.
The Vietnam war affected the United States horribly because we lost great and amazing soldiers
The answer is: effective secondary source document"
Within 20 years, historians would have enough time to gather all facts and data from all sides that involved in historical event. All of these facts and data is useful for them to decipher how the historical events were unfolded.
This make the chart an effective source to find for information regarding the event. But, since it does not made by people who actually involved in the events, it could only be considered as a secondary source.
