Complex sentence: In July 1915, the French Commander in Chief Joseph Joffre, held the first inter-Allied conference at Chantilly and in December 1915, a second conference resolved to conduct simultaneous attacks by the French, Russian, British and Italian armies.
Split into simpler sentences: In July 1915, the French Commander in Chief Joseph Joffre held the first inter-Allied conference at Chantilly. In December, a second conference resolved to conduct simultaneous attacks by the French, Russian, British and Italian armies.