Why are primary sources valuable to historians?

Me asap with these two questions about wwi 20 points will be rewarded.1. what is the significance of the battle of somme? 2. how many years into the war did it take for germany to use poison gas on a large-scale?

Asap 50 choose one civil war topic! write a report of at least 400 words -a major civil war battle -civil war munitions and uniforms -the emancipation proclamation -the gettysburg adress make sure to correctly cite your research source or sources in your writing!

What states were considered part of the antebellum south?