Pope Innocent IV in the context of "Siegfried III (archbishop of Mainz)"

Frederick II (Italian: Federico, Sicilian: Fidiricu, German: Friedrich, Latin: Fridericus; 26 December 1194 – 13 December 1250) was King of Sicily from 1198, King of Germany from 1212, King of Italy and Holy Roman Emperor from 1220 and King of Jerusalem from 1225. He was the son of Emperor Henry VI of the Hohenstaufen dynasty (the second son of Emperor Frederick Barbarossa) and Queen Constance I of Sicily of the Hauteville dynasty.

Frederick was one of the most brilliant and powerful figures of the Middle Ages and ruled a vast area, beginning with Sicily and stretching through Italy all the way north to Germany. Viewing himself as a direct successor to the Roman emperors of antiquity, he was Emperor of the Romans from his papal coronation in 1220 until his death; he was also a claimant to the title of King of the Romans from 1212 and unopposed holder of that monarchy from 1215. As such, he was King of Germany, of Italy, and of Burgundy. At the age of three, he was crowned King of Sicily as co-ruler with his mother, Constance, Queen of Sicily, the daughter of Roger II of Sicily. His other royal title was King of Jerusalem by virtue of marriage and his connection with the Sixth Crusade. Frequently at war with the papacy, which was hemmed in between Frederick's lands in northern Italy and his Kingdom of Sicily (the Regno) to the south, he was "excommunicated four times between 1227 and his own death in 1250", and was often vilified in pro-papal chronicles of the time and after. Pope Innocent IV went so far as to declare him preambulus Antichristi (forerunner of the Antichrist).

The Seventh Crusade (1248–1254) was the first of the two Crusades led by Louis IX of France. Also known as the Crusade of Louis IX to the Holy Land, it aimed to reclaim the Holy Land by attacking Egypt, the main seat of Muslim power in the Near East. The Crusade was conducted in response to setbacks in the Kingdom of Jerusalem, beginning with the loss of the Holy City in 1244, and was preached by Innocent IV in conjunction with a crusade against emperor Frederick II, Baltic rebellions and Mongol incursions. After initial success, the crusade ended in defeat, with most of the army – including the king – captured by the Muslims.

Following his release, Louis stayed in the Holy Land for four years, doing what he could towards the re-establishment of the kingdom. The struggle between the papacy and Holy Roman Empire paralyzed Europe, with few answering Louis' calls for help following his capture and ransoming. The one answer was the Shepherds’ Crusade, started to rescue the king and meeting with disaster. In 1254, Louis returned to France having concluded some important treaties. The second of Louis' Crusades was his equally unsuccessful 1270 expedition to Tunis, the Eighth Crusade, where he died of dysentery shortly after the campaign landed.

The Rurik dynasty, also known as the Rurikid or Riurikid dynasty, as well as simply Rurikids or Riurikids, was a noble lineage allegedly founded by the Varangian prince Rurik, who, according to tradition, established himself at Novgorod in the year 862. The Rurikids were the ruling dynasty of Kievan Rus' and its principalities following its disintegration.

The Romanovichi ruled the southwestern territories, which were unified by Roman the Great and his son Daniel, who was in 1253 crowned by Pope Innocent IV as the king of Ruthenia. Galicia–Volhynia was eventually annexed by Poland and Lithuania. The northern and northeastern territories were unified by the Daniilovichi of Moscow; by the 15th century, Ivan III threw off the control of the Golden Horde and assumed the title of sovereign of all Russia. Ivan IV was crowned as the tsar of all Russia, where the Rurik line ruled until 1598, following which they were eventually succeeded by the House of Romanov.

The "Sicilian business" is a historiographical term used to describe the failed attempt by Henry III of England to claim the Kingdom of Sicily for his son Edmund, who had been offered the throne by the papacy. Sicily, established in the twelfth century as a theoretical papal fief, had been ruled by Holy Roman Emperor Frederick II from 1198 until his death in 1250; Pope Innocent IV now sought to install an agreeable sovereign to succeed his longtime adversary. After failed negotiations with Edmund's uncles Richard of Cornwall and Charles of Anjou, the papacy formally offered the throne to the English prince in 1254. For the project, Henry III was tasked with delivering Edmund and armed forces to Sicily to claim it from Manfred, who was serving as regent for Frederick II's grandson Conradin; the papacy was to offer assistance.

A strategic marriage was planned for Edmund; potential brides were the dowager queen of Cyprus or a daughter of Manfred in order to resolve the dispute over the kingdom. Neither union came to fruition, and despite continued attempts to secure support and financing, Henry III's efforts to establish Edmund as the Sicilian monarch faced numerous setbacks. Pope Alexander IV, who had succeeded Innocent IV in 1254, was no longer in a position to effectively finance the project, demanding payment from Henry III as compensation for the papacy's contributions to the campaign. Finding only minimal support from Parliament and faced with the threat of excommunication from Rome, Henry III resorted to extorting money from his domestic clergy in an attempt to pay the debts. The "Sicilian business" became entangled with broader political troubles in England, and the project ultimately collapsed. Pope Urban IV formally revoked the grant of the Kingdom of Sicily to Edmund in 1263 and instead consigned it to Charles of Anjou, who successfully assumed control of the kingdom in 1266.

There were many imperial interregna in the history of the Holy Roman Empire, when there was no emperor. Interregna in which there was no emperor-elect (king of the Romans) were rarer. Among the longest periods without an emperor were between 924 and 962 (38 years), between 1250 and 1312 (62 years), and between 1378 and 1433 (55 years). The crisis of government of the Holy Roman Empire and the German kingdom thus lasted throughout the late medieval period, and ended only with the rise of the House of Habsburg on the eve of the German Reformation and the Renaissance. The term Great Interregnum is occasionally used for the period between 1250 (death of Frederick II) and 1273 (accession of Rudolf I).

After the deposition of Frederick II by Pope Innocent IV in 1245, Henry Raspe, Landgrave of Thuringia was set up as anti-king to Frederick's son Conrad IV (d. 1254). Frederick’s "deposition" was widely regarded as illegitimate, and no monarch in Europe offered any meaningful support for Innocent in his crusade against the emperor—whose immense status and legendary reputation as perhaps the greatest monarch of his day continued undiminished, especially in the vast Hohenstaufen core holdings. In Germany, particularly in Swabia, most of Franconia and the south, Hohenstaufen power remained formidable and the papal cause could only rely on the support of the major ecclesiastical princes. The secular princes of Germany were variably loyal to the Hohenstaufen or took a neutral stance. Henry Raspe was killed in 1247 and succeeded as anti-king by William of Holland (died 1256). Throughout 1249-1250 Conrad IV had steadily defeated William, whose power never extended beyond a tenuous hold north of the Rhine, and extracted a truce from the major ecclesiastical princes. Everywhere, papal crusade against the Hohenstaufen appeared to be disintegrating. By Frederick II’s death in late 1250, the emperor controlled most of Italy and his son enjoyed a relatively solid base across southern and central Germany. The Hohenstaufen remained the most prestigious, powerful and preeminent dynasty in Europe. However, buoyed by Frederick’s death, the papacy remained intransigent and Conrad IV was unable to secure the imperial mantle and died of malaria near Rome in 1254 while consolidating his Sicilian inheritance in southern Italy. Conrad’s death and the extreme youth of his son, Conradin, signaled an implosion in the Hohenstaufen dynastic power and after the 1257 imperial election, the crown was contested between Richard of Cornwall, who was supported by the Guelph party, and Alfonso X of Castile, who was recognized by the Hohenstaufen party but never set foot on German soil. After Richard's death in 1273, Rudolf I of Germany, a minor pro-Staufen count, was elected. He was the first of the Habsburgs to hold a royal title, but he was never crowned emperor. Alfonso hold on to his claim to the throne until 1275. After Rudolf's death in 1291, Adolf and Albert were two further weak kings who were never crowned emperor starting a line of so-called count-kings which lasted to the establishment of a de facto hereditary monarchy by the Habsburgs in the 15th century.

The Imperial Seal of the Mongols is a seal (tamgha) that was used by the Mongols. The imperial seals, bearing inscriptions in Mongolian script or other scripts, were used in the Mongol Empire, the Yuan dynasty, and the Northern Yuan dynasty, among others.

According to Plano Carpini, the Russian handicraftsman, Kozma, made a seal for Güyük Khan. This seal might have been a seal used to stamp the letter to Pope Innocent IV.