The Kingdom of Denmark, in Look to the West, has had quite an interesting 18th century. History diverged from OTL after Crown Prince Frederick (Christian VI's son) died in 1743. The kingdom thence passed to Prince Christian, who became Christian VII. Christian VII was a reformer who turned against his father's absolutist and Pietist policies, sold off Denmark's global interests and used the payments to finance a grand effort aimed at dominance of the Baltic. He did not live to see his work completed, but completed it was. In 1800 Sweden was joined once more to Denmark in a new Union of Kalmar.
Generally, Denmark in the 18th century has pursued a pro-British, pro-Russian, anti-French and anti-Dutch foreign policy. Danish help in the Great Baltic War both resulted in the new union with Sweden and also secured the duchy of Oldenburg under complete Danish control, the Russian tsar relinquishing his claims.
Christian VII restored the Danish Diet, shortly after abolishing serfdom, in order to play off the people against rebellious nobles. He also abolished the slave trade as a sop to Danish intellectuals, having already sold off all Denmark's slave trading posts to the Dutch anyway.
1699-1730: Frederik IV
1730-1745: Christian VI
1745-1787: Christian VII
1787-1813: Johannes II (also John IV of Sweden)
1813-1835: Valdemar V (also Valdemar II of Sweden); in 1835 he proclaimed himself Valdemar I of a new united Nordic Empire.
1835-1847: Valdemar I
1847-1861: Frederick I
1861-1880: Christian I
1880-????: Valdemar II
Until the union with Sweden in 1800, Denmark used the familiar Dannebrog, the white Scandinavian cross on red:
The Dannebrog remains in regular use, but officially Denmark now uses a flag which incorporates the Danish-Swedish Union Jack in the canton: