Complex sentence: With the outbreak of World War I, Lejeune assumed command of the newly constructed Marine Barracks, Quantico, Virginia; however, his overseas service was inevitable, and in June 1918, he arrived at Brest, France.
Split into simpler sentences: With the outbreak of World War I, Lejeune assumed command of the newly constructed Marine Barracks, Quantico, Virginia. However, his overseas service was inevitable, and in June 1918, he arrived at Brest, France.