From 1764 to 1776, there was a political crisis regarding the authority of the British Parliament over America. Yet the British case for parliamentary sovereignty was not particularly clear, and by 1774, most Americans argued that Parliament had no authority over internal affairs in America. Even English politicians and lawyers, such William Pitt the Elder and Lord Camden, argued that Parliament had no ability to tax the American colonies. In 1776, the American colonies declared their independence and a war of independence ensued, that Britain lost. But what could explain this disagreement over sovereignty? This chapter looks to several factors for explanation. These include the fact of Britain’s uncodified Constitution, which rendered it unclear which laws were in any case ‘constitutional’. There was also disagreement as to how the British Constitution applied in the colonies. Many Americans asserted that only a shared monarch connected American colonies legally to Britain and to each other, and that colonial assemblies were comparable to Parliament. There was, however, no acceptance of this in Britain, where the doctrine of undivided and unlimited sovereignty was increasingly employed by those in power.