Complex sentence: Upon his return to Italy in 1913 he is promoted to lieutenant and at the end of the year is assigned to the 2nd Infantry Battalion of Libya where he remains until January of 1915 at which time he is repatriated to Italy.
Split into simpler sentences: Upon his return to Italy in 1913 he is promoted to lieutenant. At the end of the year is assigned to the 2nd Infantry Battalion of Libya where he remains until January of 1915 at which time he is repatriated to Italy.