With the Erfurter Division Treaty of 1572 the remaining lands were eventually and forcibly divided between the sons of the defeated John Frederick II.
 The younger son was John William of Saxe-Weimar, who received, among other properties, the cities of Jena, Altenburg and Saalfeld.
Because the elder son, John Frederick II “the Middle” was still in prison for life in Austria, his sons, John Casimir and John Ernest, were given the new Principality of Saxe-Coburg, with Coburg chosen as their residence and “Duke” as their titles.
 The Principality consisted of the southern and western parts of Thuringia, including the cities of Eisenach, Gotha and Hildburghausen.
 One of the guardians for the sons was the enemy of their father, Augustus, Elector of Saxony, who supervised their education and who, for his own reasons, began in Coburg a corrupt Regency with Saxon officials from his Electorate.

Only after the death of Elector Augustus of Saxony in 1586 were Duke John Casimir and his brother John Ernest able to take over the government of their Principality.
 In 1596, the Principality was cut in half to give John Ernest his own Duchy of Saxe-Eisenach and John Casimir remained in Coburg to reign alone.
 His remaining territories were the Districts of Coburg, with the jurisdictions of Lauter, Rodach and Gestungshausen; Heldburg with the jurisdictions of Hildburghausen, Römhild, Eisfeld, Schalkau, Sonneberg, Neustadt bei Coburg, Neuhaus am Rennweg, and Mönchröden; and Sonnefeld.
 Under the reign of John Casimir, there was a building boom in Coburg.
 Above all, he established as the nucleus of Coburger government an administrative apparatus that would survive for a long time after his death and through many wars and political upheavals.
 Casimir, the founder of the Coburger State, died in 1633.
 His Principality then fell to his brother, the Duke of Saxe-Eisenach, John Ernest, who was also childless.
 During this time, the Coburger Land was hit hard by the Thirty Years War as the staging area for numerous armies.
 The population fell from 55,000 to 22,000.
With the Erfurter Division Treaty of 1572 the remaining lands were eventually and forcibly divided between the sons of the defeated John Frederick II.  The younger son was John William of Saxe-Weimar, who received, among other properties, the cities of Jena, Altenburg and Saalfeld. Because the elder son, John Frederick II “the Middle” was still in prison for life in Austria, his sons, John Casimir and John Ernest, were given the new Principality of Saxe-Coburg, with Coburg chosen as their residence and “Duke” as their titles.  The Principality consisted of the southern and western parts of Thuringia, including the cities of Eisenach, Gotha and Hildburghausen.  One of the guardians for the sons was the enemy of their father, Augustus, Elector of Saxony, who supervised their education and who, for his own reasons, began in Coburg a corrupt Regency with Saxon officials from his Electorate.
Only after the death of Elector Augustus of Saxony in 1586 were Duke John Casimir and his brother John Ernest able to take over the government of their Principality.  In 1596, the Principality was cut in half to give John Ernest his own Duchy of Saxe-Eisenach and John Casimir remained in Coburg to reign alone.  His remaining territories were the Districts of Coburg, with the jurisdictions of Lauter, Rodach and Gestungshausen; Heldburg with the jurisdictions of Hildburghausen, Römhild, Eisfeld, Schalkau, Sonneberg, Neustadt bei Coburg, Neuhaus am Rennweg, and Mönchröden; and Sonnefeld.  Under the reign of John Casimir, there was a building boom in Coburg.  Above all, he established as the nucleus of Coburger government an administrative apparatus that would survive for a long time after his death and through many wars and political upheavals.  Casimir, the founder of the Coburger State, died in 1633.  His Principality then fell to his brother, the Duke of Saxe-Eisenach, John Ernest, who was also childless.  During this time, the Coburger Land was hit hard by the Thirty Years War as the staging area for numerous armies.  The population fell from 55,000 to 22,000.
Saxe-Coburg