Danmarks Riges Grundlov (English: The constitution of the Danish Realm) is a decision available to 
Denmark.
One requires to have researched State & Government and have an average militancy below 3.0. It changes the voting reform to Only Landed, the Government type to HM's Government and give Denmark 5 prestige.
The description in the politics tab says: Denmark had been an absolute monarchy since 1660 when, on June fifth 1849, King Frederick VII signed the document known as 'Danmarks Riges Grundlov', The Danish Constitution, into law. The signing of a constitution delimiting the monarch's power, a development which Fredericks predecessors had fought hard to avoid, came about during a period of Danish national unity, following the First Schleswig War. The Constitution marks Denmark's transition away from absolutism, and to a constitutional monarchy. Let us give our people a constitution!