Complex sentence: Sir Alexander Leslie was badly wounded in the winter of I632, but was promoted again in 1636 to the rank of field marshal, but by 1638 events in England compelled him to return to Scotland to lead the army of the Covenanters in the Bishops Wars.
Split into simpler sentences: Sir Alexander Leslie was badly wounded in the winter of 1632, but in 1636 he was appointed Field Marshal. In 1638 events in England compelled him to return to Scotland to lead the army of the Covenanters in the Bishops Wars.