Complex sentence: Hitler's rise to prominence came as a surprise to Hess and many of his colleagues from the regiment, as the future dictator had been something of a non-entity, with no friends within the regiment and little interaction with others.
Split into simpler sentences: Hitler's rise to prominence came as a surprise to Hess and many of his colleagues from the regiment. The future dictator had been something of a non-entity during his time in the army, with no friends within the regiment and little interaction with others.