Complex sentence: Thanks to his older brother Lawrence's connection to the prominent Fairfax family, Washington was appointed official surveyor for Culpeper County, a well-paid position which enabled him to purchase land in the Shenandoah Valley, the first of his many land acquisitions in western Virginia.
Split into simpler sentences: Thanks to his older brother Lawrence's connection to the prominent Fairfax family, Washington had been appointed to this well-paid official position. He was subsequently able to purchase land in the Shenandoah Valley, the first of his many land acquisitions in western Virginia.