Lord North's government was chiefly concerned with discontent in America. To assuage American opinion most of the custom duties were withdrawn, except for the tea duty, which in George's words was "one tax to keep up the right levy taxes". In 1773, the tea ships moored in Boston Harbor were boarded by colonists and the tea was thrown overboard, an event that became known as the Boston Tea Party. In Britain, opinion hardened against the colonists, with Chatham now agreeing with North that the destruction of the tea was "certainly criminal". With the clear support of Parliament, Lord North introduced measures, which were called the Intolerable Acts by the colonists: the Port of Boston was shut down and the charter of Massachusetts was altered so that the upper house of the legislature was appointed by the Crown instead of elected by the lower house. Up to this point, in the words of Professor Peter Thomas, George's "hopes were centred on a political solution, and he always bowed to his cabinet's opinions even when sceptical of their success. The detailed evidence of the years from 1763 to 1775 tends to exonerate George III from any real responsibility for the American Revolution." Though the Americans characterised George as a tyrant, in these years he acted as a constitutional monarch supporting the initiatives of his ministers.