The meeting was called together because the Articles of Confederation were proving to be a very loose form of government. Congress, under the Articles, lacked the ability to regulate trade, particularly tariffs. Newly formed states were treating each other as countries in and of themselves rather than the distinct, but joined bodies as they are recognized today. The Maryland and Virginia governments saw this issue, and decided to take it upon themselves to create an agreement that defined the rights and usage of shared waterways.
This was one step in many that led to the downfall of the Articles of Confederation that would happen in the summer of 1787. The fact that tariffs and taxes were one of very few ways that the early American government could bring in revenue only compounded the matter. Other factors that would play into the collapse of the Articles would take place in the remainder of 1785 and 1786 before Congress called together the meeting in Philadelphia that would become the Constitutional Convention.
|A selection of the objections discussing the composition of the legislature.|
It is impossible to say for sure, but it is likely that Mason's concerns on this topic, especially the political, were colored by his participation in the Mount Vernon Conference in March of 1785. For southern plantation owners like Mason, navigation and commerce would also have significant personal implications as they relied on northern states for shipbuilding and manufactured goods. Virginia, specifically, shared significant waterways with Maryland, and those concerns would also need to be addressed under the newly structured government as laid out by the Constitution.