Complex sentence: The advance guard of 300 grenadiers and colonials with two cannon under Lieutenant Colonel Thomas Gage began to move ahead, and unexpectedly came upon the French and Indians, who were hurrying to the river, behind schedule and too late to set an ambush.
Split into simpler sentences: The advance guard of 300 grenadiers and colonials with two cannon under Lieutenant Colonel Thomas Gage began to move ahead. Then, unexpectedly came upon the French and Indians, who were hurrying to the river, behind schedule and too late to set an ambush.