Complex sentence: He was Treasurer of Scotland from 1630-36, but his strong support of the Stewart dynasty led him into financial difficulty, compelling him to sell Dalkeith to the Earl of Buccleuch in 1642.
Split into simpler sentences: He was Treasurer of Scotland from 1630-36, and a strong supporter of the Stewart dynasty. However, he was forced to spend much of his fortune in the royal interest, leading him into financial difficulty, and compelling him to sell Dalkeith to the Earl of Buccleuch in 1642.