What significant declaration was introduced on 26 August 1789?

The significant declaration introduced on 26 August 1789 is the Declaration of the Rights of Man and Citizen. This foundational document emerged from the principles of the French Revolution, encapsulating the Enlightenment ideas of individual rights, liberty, and equality. It asserted that all men are born free and equal in rights and laid the groundwork for modern human rights concepts. This declaration emphasized the importance of natural rights, the rule of law, and the sovereignty of the people, making it a key milestone in the establishment of a more democratic society in France.

The other options, while important to the revolutionary timeline, do not correspond to the specified date. The Tennis Court Oath took place earlier in June 1789 and represented the members of the Third Estate's commitment to drafting a new constitution. The August Decrees were enacted shortly after the Declaration, in early August 1789, to abolish feudal privileges. The Constitution of 1791 was completed later as France transitioned toward a constitutional monarchy.