Complex sentence: For two days, the French could not catch up with their adversaries but on the afternoon of 28 November, their light cavalry found the "Army of the Left" camped at Alba de Tormes.
Split into simpler sentences: For two days, the French were unable to catch up with their adversaries. But on the afternoon of 28 November, their light cavalry found the "Army of the Left" camped at Alba de Tormes.