Complex sentence: At the outbreak of the First World War, the leading global exporter of nitrates for gunpowder was Chile, which maintained her neutrality and provided nearly all America's nitrates requirements, which was also the principal ingredient of chemical fertilizer in farming.
Split into simpler sentences: At the outbreak of the First World War, the leading global exporter of nitrates for gunpowder was Chile. Chile had maintained neutrality during the war and provided nearly all America's nitrate requirements, as it was also the principal ingredient of chemical fertilizer in farming.