Complex sentence: Whereas at the beginning of the war both the German and French armies numbered well over a million men each, divided into eight and five field armies, respectively, the BEF initially numbered only about 80,000 soldiers divided into two corps.
Split into simpler sentences: Whereas at the beginning of the war both the German and French armies numbered well over a million men each, divided into eight and five field armies, respectively. The BEF initially numbered only about 80,000 soldiers divided into two corps.