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50:1 Western Historical Quarterly 17-42


Like a historical mantra repeated time and again, it is asserted that the Louisiana Purchase doubled the size of the United States. As this assertion takes for granted that the Purchase included the entire Missouri watershed, it rests on the assumption that France had a valid title thereto because, as a matter of common sense and international law, France could only convey title to territory that it actually owned. But what basis is there for the assumption that France had sovereign title to the vast territory drained by the Missouri River that stretches from the Mississippi River to the Rocky Mountains? In actual fact, at the time of the Purchase in 1803 most of that territory had not even been explored, let alone possessed, by the French – it was occupied and controlled by many Indian nations, over whom France exercised no authority. As France clearly did not exercise de facto sovereignty over the Missouri watershed, any claim it had to the vast territory would have had to be a claim to de jure sovereignty based on law that did not depend on actual occupation and control. If so, what system of law could have given France legal title to this immense territory, most of which no Frenchman had ever laid eyes on?

This article will probe, and attempt to answer, the troubling and too often neglected question of France’s title to the Missouri watershed. Our discussion and analysis will rely on the vital distinction between de facto and de jure sovereignty. Assessing claims to de facto sovereignty is an empirical matter that depends on actual possession, control, and exercise of authority on the ground. As such, it is a subject for historical investigation. Assessment of claims to de jure sovereignty, on the other hand, necessarily involves deciding at the outset which body of law to apply, which raises a normative issue of moral and political philosophy: Which body of law should apply in the circumstances? Once that has been determined, a de jure assessment entails legal analysis in accordance with relevant principles and rules from the chosen body of law. While this analysis will obviously take known historical facts into account, it must be kept clearly in mind that, unlike de facto sovereignty, de jure sovereignty is a matter of mixed fact and law, not to be determined by historical methodology alone. In other words, it depends on the application of a particular body of legal rules to ascertained facts. This article will critically assess the validity of France’s claim to territorial sovereignty over the Missouri watershed from both a de facto and a de jure perspective. This assessment will lead to a re-evaluation of the geographical extent of the Louisiana Purchase on the Northern Plains.


This is a post-print of the final published paper.