Complex sentence: Arimondi, who had previously advanced to Aderà, away, was stopped by a telegram from Baratieri and was forced to retreat, leaving Toselli and Giuseppe Galliano to fend for themselves at the Battle of Amba Alagi and the Battle of Mek'ele.
Split into simpler sentences: Arimondi, who had previously advanced to Aderà, away, was stopped by a telegram from Baratieri and forced to retreat. This left Toselli and Galliano to fend for themselves at the Battle of Amba Alagi and the Battle of Mek'ele.