Answer:
Written sources. Some examples of primary written sources are contemporary letters, eyewitness accounts, official documents, political declarations and decrees, administrative texts, and histories and biographies written in the period that is to be studied. Written sources help in cross-checking data or information collected from oral and other sources of historical knowledge. This help to reach reliable conclusions. Documents provide more detailed information than oral sources, e.g. dates, illustrative pictures, names of participants in events
Explanation:
Railroads played an absolutely crucial role in the Industrial Revolution, since they made for the incredibly fast transfer of goods such as iron and steel that were used to build things--not to mention the transport of the workers themselves.
Well, from looking at the chart, it seems that there's a huge loss of life on the "winning" side. I believe the people of those countries must've felt emotionally and economically defeated. Considering the great amount of lives lost during the war, I'd say it would effect the society emotionally and there'd be fewer people around. And during wars countries usually use lots of money and weaponry to fund the cause, so those nations must've been in a huge economic crisis once the war ended. <span />
