Complex sentence: Knowing that he did not have sufficient strength to capture the city, Early demonstrated outside Fort Stevens and Fort DeRussy, and there was skirmishing and artillery duels on July 11 and July 12.
Split into simpler sentences: Knowing that he did not have sufficient strength to capture the city, Early led skirmishes at Fort Stevens and Fort DeRussy. The opposing forces also had artillery duels on July 11 and July 12.