From 1738 to 1793, Oxford rose as a major trading center and then collapsed as its trade with England was cut off and the new nation reorganized commerce. Robert Morris Sr. arrived from Liverpool in 1738 as chief factor for Foster Cunliffe & Sons and supervised trade in tobacco, pork, hides, and lumber, leading Oxford's first great economic boom. In 1742, 355 enslaved Africans were brought directly to Oxford aboard the ship London Friggot, and in 1747 Morris imported 106 indentured Scottish prisoners taken at the Battle of Culloden to work on Oxford's tobacco plantations. Morris died in 1750 after being accidentally struck by debris from a saluting cannon on the arriving ship Liverpool Merchant and was buried at White Marsh Churchyard in Trappe. By the 1760s, most Eastern Shore plantations had shifted from labor-intensive and falling tobacco cultivation to wheat, while Oxford had become a cosmopolitan trading center second only to Annapolis in the amount and variety of imported goods. The Barnaby House was built on High Street in 1770 as the only colonial house in Oxford surviving on its original foundation, and in 1770–71 slave ships arriving in Oxford unloaded 226 persons from Senegal. After thirty trans-Atlantic trading voyages for a London firm, Captain Jeremiah Banning retired in 1773 to his Oxford estate, The Isthmus, as their Eastern Shore agent. As Britain blockaded Boston Harbor and deployed troops in Massachusetts in 1774, American colonists gathered for the First Continental Congress in Philadelphia. On September 11, 1775, the last British ship departed Oxford, ending nearly a century of profitable European trade; that year Colonel Trench Tilghman of Oxford became one of George Washington's aides-de-camp, and after Concord, Lexington, and Bunker Hill, Washington took command of the new Continental Army. Congress adopted the Declaration of Independence on July 4, 1776. The Treaty of Paris was signed in 1783 to end the war with Great Britain, and Annapolis became the nation's capital for ten months from November 1783 until August 1784. In 1784 Congress ratified the treaty, officially recognizing the United States as an independent and sovereign nation, and Maryland's constitution formally prohibited the transportation of slaves from Africa. A new constitution for the United States of America was drawn up by Congress in 1787, and George Washington was elected first President of the United States in 1789. By 1790, Oxford's economy was in ruins, its population had fallen to 98, and only 13 houses remained. In 1791 Washington appointed Jeremiah Banning the first official Customs officer of the United States, with his Customs House at The Isthmus across the Tred Avon River from Oxford on Plain Dealing Creek; that year three quarters of the states approved 10 amendments to the U.S. Constitution guaranteeing individual freedoms, and Maryland donated land for the new national capital, Washington, D.C. In 1793, Banning lamented that Oxford looked more like an uninhabited island than a place where human feet had ever trod.