He moved to the capital of East Florida at St. Augustine and resided in the Governor's House. He ended Indian raids with the Treaty of Fort Picolata in attempts at maintaining peaceful relations between American Indian groups and Florida colonists and to entice future immigrants to his colony. During the Anglo-Cherokee War of 1759–1761, Grant had become familiar with systems of gift exchange and reciprocity used by Southeast Indian groups, which he sought to implement in Florida. Grant also established the Florida-Georgia border. Grant's ventures were ultimately profitable, but most attempts failed to produce results. He encouraged new agriculture, setting up trade in cotton, indigo, timber, and cochineal. He personally gained and developed several plantations as grants. Then, in 1771, illness forced him to return to England. Patrick Tonyn replaced him as governor. Grant appointed Dr. David Yeats, the Secretary of the Colony, to manage his plantations in his absence. Yeats' letters to Grant concerning the properties have long interested Florida colonial historians. Back home in Scotland, Grant was elected to Parliament in 1773 as an MP for Tain Burghs. In the period leading up to the American Revolutionary War, he became one of the most outspoken of the anti-American members. In a speech early in 1775, he remarked that the colonists "...could not fight...", and declared that he could "go from one end of America to other and geld all the males." By the summer of 1775, he was returned to active service, and Colonel Grant was ordered to America. He arrived in Boston on 30 July. In the aftermath of the Battle of Bunker Hill, he urged General Gage to move the troops to New York City, to have room to manoeuvre. His advice was ignored at the time, and he remained as a supernumerary until December, when he was made colonel and commander of the 55th Regiment of Foot. He would hold that command until 1791. His prediction that Boston was an untenable position was proved correct the following spring, and, on 17 March 1776, he accompanied the general withdrawal to Halifax, Nova Scotia . By the summer of 1776, General William Howe had replaced Gage as commander, and took Grant's advice about New York. Grant was given the provisional rank of major-general, and played several key parts in Howe's movements. Fortunately for the Americans, Howe refused advice from Grant, who proposed burning Boston, Marblehead, New York, and Philadelphia.