Complex sentence: At the outset of the civil war Wentworth was with George Goring in Portsmouth, but after the fall of that garrison he joined the king's main field army, and as Lord Wentworth raised a company of dragoons.
Split into simpler sentences: At the outset of the civil war, Wentworth was with George Goring in Portsmouth. After the fall of that garrison, he joined the King's Main Field Army, and as Lord Wentworth, raised a company of dragoons.