The correct answer for the box with the question mark is C. Constitutional Convention.
Shays's Rebellion exposed the weaknesses of the Articles of Confederation, leading to the realization that a stronger central government was needed.
The Constitutional Convention was convened in 1787 to address these issues and ultimately resulted in the drafting of the United States Constitution.
The other options, War of 1812, Louisiana Purchase, and Declaration of Independence, are significant events in American history, but they are not directly related to the need for a new constitution following Shays's Rebellion.