Question: The union Eric of Pomerania was king of joined how many kingdoms under a single monarch?

Context paragraphs:
Dasarna Kingdom: Dasarna Kingdom was one of the many kingdoms ruled by Yadava kings in medieval central and western India.  It lay to the south of the Chedi and Panchala kingdoms, in northern Madhya Pradesh.  The Panchala prince Sikhandi married a princess from Dasarna.  Sikhandin was alleged to be 'one of the neuter-gender'.  This led to a dispute between the Dasarna king and the Panchala king Drupada.

Union of the Crowns: The Union of the Crowns (Scottish Gaelic: "Aonadh nan Crùintean" ; Scots: "Union o the Crouns" ) was the accession of James VI of Scotland to the thrones of England and Ireland, and the consequential unification for some purposes (such as overseas diplomacy) of the three realms under a single monarch on 24 March 1603.  The Union of Crowns followed the death of Elizabeth I of England — the last monarch of the Tudor dynasty, who was James's unmarried and childless first cousin twice removed.

House of Griffins: The House of Griffins or House of Pomerania (German: "Greifen" ; Polish: "Gryfici" ), also known as "House of Greifen", was a dynasty of dukes ruling the Duchy of Pomerania from the 12th century until 1637.  The name "Griffins" was used by the dynasty after the 15th century and had been taken from the ducal coat of arms.  Wartislaw I (around 1091 – died August 9, 1135) was the first historical ruler of the Duchy of Pomerania and the founder of the Griffin dynasty.  The most prominent Griffin was Eric of Pomerania, who became king of the Kalmar Union in 1397, thus ruling Denmark, Sweden and Norway.  The last Griffin duke of Pomerania was Bogislaw XIV, who died during the Thirty Years' War, which led to the division of Pomerania between Brandenburg-Prussia and Sweden.  Duchess Anna von Croy, daughter of Duke Bogislaw XIII and the last Griffin, died in 1660.

Engelbrekt rebellion: The Engelbrekt rebellion was a rebellion in 1434–1436 led by Swedish nobleman Engelbrekt Engelbrektsson against Eric of Pomerania, the king of the Kalmar Union.  It resulted in the deposing of Eric as well as erosion of the union.

Kalmar Union: The Kalmar Union or Union of Kalmaris (Danish, Norwegian and Swedish: "Kalmarunionen" ; Latin: "Unio Calmariensis" ) was a personal union that from 1397 to 1523 joined under a single monarch the three kingdoms of Denmark, Sweden (then including parts of Finland), and Norway, together with Norway's overseas dependencies (then including Iceland, Greenland, the Faroe Islands and the Northern Isles).  The Union was not quite continuous; there were several short interruptions.  Legally the countries remained separate sovereign states, but with their domestic and foreign policies being directed by a common monarch.

List of current sovereign monarchs: A monarch is the head of a monarchy, a form of government in which a state or polity is ruled by an individual who normally rules for life or until abdication, and typically inherits the throne by birth.  Monarchs may be autocrats (as in all absolute monarchies) or may be ceremonial figureheads, exercising only limited or no reserve powers at all, with actual authority vested in a legislature and/or executive cabinet (as in many constitutional monarchies).  In many cases, a monarch will also be linked with a state religion.  Most states only have a single monarch at any given time, although a regent may rule when the monarch is a minor, not present, or otherwise incapable of ruling.  Cases in which two monarchs rule simultaneously over a single state, as is the current situation in Andorra, are known as coregencies.

Unification of Nepal: Before Shah dynasty took over Nepal, Nepal was limited to Kathmandu valley and surrounding territories which consist many kingdoms.  After conquering the valley in the mid-eighteenth century, King Prithvi Narayan Shah moved his ruling state to Nepal from Gorkha.  He then started his conquering campaign with the banner of Nepal than Gorkha.

Saurashtra Kingdom: Saurashtra kingdom in the epic Mahabharata is one among the many kingdoms ruled by Yadava kings in the central and western India.  Other kingdoms in this group include Chedi Kingdom, Dasarna Kingdom, Surasena Kingdom or Vraja Kingdom, Karusha Kingdom, Kunti Kingdom, Avanti Kingdom, Malava Kingdom, Gurjara Kingdom, Anarta Kingdom, Dwaraka Kingdom, Heheya Kingdom and Vidarbha Kingdom.

Eric of Pomerania: Eric of Pomerania KG (1381 or 1382 – 24 September 1459) was King Eric (Eirik) III of Norway (1389–1442), King Eric VII of Denmark (1396–1439), and King Eric ("Ericus") of Sweden (1396–1439), in all three known mainly as "Erik af/av Pommern".  He was the first King of the Nordic Kalmar Union, succeeding his adoptive mother Margaret I of Denmark, and was also Duke Eric I of Pomerania.

Emblems of the Kalmar Union: The Kalmar Union was the personal union of the kingdoms of Denmark, Norway and Sweden during the 15th century.  The first king of the Kalmar Union was Eric of Pomerania.  His seal combined the coats of arms of Norway (center, as an inescutcheon upon a cross over all), Denmark (in dexter chief), Sweden (the Folkung lion, in dexter base) and Pomerania (a griffin, in sinister base), and in addition the Three Crowns symbol in sinister chief; the latter heraldic design predates the Kalmar Union, and is now mostly associated with the coat of arms of Sweden, but which during the 15th century came to represent the three kingdoms of the union.

Supporting paragraphs: Engelbrekt rebellion Kalmar Union
Answer: three