Complex sentence: Of the powers, only Britain did not have conscription, and France had instituted conscription during the Revolutionary Wars, and, between 1913 and the outbreak of the war, France increased her conscription time from 2 years to 3.
Split into simpler sentences: Of the powers, only Britain did not have conscription, and France had instituted conscription during the Revolutionary Wars. Between 1913 and the outbreak of the war, France increased her conscription time from 2 years to 3.