Complex sentence: Two other companies from the 9th cavalry were in the area and proceeded to the battlefield, when the reinforcements entered the canyon Victorio's warriors ceased firing until the Americans began a flanking maneuver towards the ridge.
Split into simpler sentences: Two other companies from the 9th cavalry were in the area and proceeded to the battlefield. When the reinforcements entered the canyon, Victorio's warriors ceased firing until the Americans began a flanking maneuver towards the ridge.