Complex sentence: At the beginning of 1914, Ilić and Stojanović became, respectively, the president and the vice-president of National Unity, which numbered 34 members, including four Muslims and four Croats.
Split into simpler sentences: At the beginning of 1914, Ilić and Stojanović became, respectively, the president and the vice-president of National Unity. It then numbered 34 members, including four Muslims and four Croats.