Complex sentence: In 1914 he joined the Foreign Legion in France as soon as the war broke out, and in 1916 volunteered in a Russian regiment fighting on the Russian front, following a cooperation agreement between the French and Russian governments.
Split into simpler sentences: In 1914 he joined the French Foreign Legion as soon as the war broke out. In 1916 volunteered in a Russian regiment fighting on the Russian front, following a cooperation agreement between the French and Russian governments.