Complex sentence: During his first offensive in 1579 with 22,000 men he retook Polotsk, during the second, in 1580, with 29,000-strong army he took Velikie Luki, and in 1581 with a 100,000-strong army he started the Siege of Pskov.
Split into simpler sentences: During his first offensive in 1579 with 22,000 men he retook Polotsk. During the second, in 1580, with a 29,000-strong army he took Velikie Luki, and in 1581 with a 100,000-strong army he started the Siege of Pskov.