Editing John III Doukas Vatatzes (section)

== Alliance with Frederick II ==
[[File:Mitteleuropa zur Zeit der Staufer.svg|thumb|Frederick II's domains as Holy Roman Emperor and King of Sicily]]
In an attempt to save the ailing Latin empire after the joint Nicaean-Bulgarian siege of Constantinople in 1236, pope Gregory IX called for a crusade against Nicaea and wrote to John III in 1237 informing him of the impending crusader army.{{sfn|Angelov|2019|p=89}} In the face of Bulgarian neutrality, John III sought allies elsewhere, turning to the Holy Roman Emperor [[Frederick II, Holy Roman Emperor|Frederick II von Hohenstaufen]].{{sfn|Angelov|2019|pp=75, 89}} Frederick II was a hated enemy of the papacy, having already been excomunnicated by Gregory IX in 1227, and in a letter composed sometime before his second excommunication in 1239, Frederick II wrote to John III lamenting the power of the pope in the west and praising John III for the power of the Byzantine emperor over the clergy.{{sfn|Angelov|2019|pp=88–89}}

Warm relations between the two Roman empires had already begun after the [[Sixth Crusade]] (1228-1229), undertook by Frederick II to lift his first excommunication, when Frederick II received a Nicaean embassy bringing gold coins, gold-embroidered silk and horses among other gifts.{{sfn|Angelov|2019|p=89}} By 1238, the two emperors had concluded an alliance. Frederick II agreed to recognize John III as the legitimate Byzantine emperor, albeit with the title "Emperor of the Greeks"{{sfn|Angelov|2019|p=206}} (''Grecorum imperator /'' Γραικῶν βασιλεύς), in exchange for mutual aid. That same year, John III sent Nicaean troops to participate in the [[Siege of Brescia (1238)|Siege of Brescia]] and Frederick II forestalled Gregory IX's crusade headed by the Latin emperor [[Baldwin II, Latin Emperor|Baldwin II]] in north Italy, forcing the crusaders to eventually take the overland route to Constantinople in 1239.{{sfn|Angelov|2019|pp=89–90}}

In early 1240, John III's wife Irene Lascarina died, and later that year John III married Frederick II's 10 year old daughter [[Constance II of Hohenstaufen]] to cement their alliance, who took the Greek name Anna.{{sfn|Angelov|2019|p=90}} Despite the lack of children from the marriage and John III's affair with his wife's lady-in-waiting, the alliance between the two emperors continued until Frederick II's death in 1250.

After Gregory IX's death in 1241, the new pope Innocent IV continued the policies of his predecessor, and attempted to wage war on both emperors. At the [[First Council of Lyon|Council of Lyon]] in 1245, Frederick was deposed as emperor and excommunicated, for, among a multitude of other reasons, marrying his daughter to John III who was called by Innocent IV "that enemy of God and the church."<ref>[https://web.archive.org/web/20120510045457/http://www.piar.hu/councils/ecum13.htm#Bull#Bull Papal bull of excommunication of Frederick II]</ref> In the east, the pope called for another crusade against John III and entered into negotiations with the Mongols to invade Nicaea, but both efforts were unsuccessful.{{sfn|Angelov|2019|pp=95, 135}} In the west, Innocent IV was much more successful against Frederick II, defeating the imperial army at the [[Battle of Parma]] in 1248.{{sfn|Angelov|2019|p=135}} John III continued to send troops, including archers and infantryman, and subsidies to Italy via Epirus between 1247 and 1250 to aid his father-in-law, who finally triumphed over the papacy in the [[Battle of Cingoli]] in August 1250, however Frederick died of dysentery in December the same year.{{sfn|Angelov|2019|pp=135–136}}

After Frederick II's death, diplomatic activity briefly continued between the two empires, with John III's son Theodore II Doukas Laskaris delivering a memorial speech in which he admired Frederick II's struggle against the hostility of the western aristocracy and clergy.{{sfn|Angelov|2019|p=136}} Frederick's son and successor [[Conrad IV of Germany|Conrad IV]] sent an embassy to Nicaea in 1253 in order to return Constance-Anna's exiled family back to Italy, but Conrad IV and John III's deaths in 1254 ensured that a possible continuation of the imperial alliance never ensued; after Conrad's IV death, the [[Holy Roman Empire]] and the [[Kingdom of Sicily]] were divided.{{sfn|Angelov|2019|p=139–141}} Frederick's other son [[Manfred, King of Sicily|Manfred]], the last Hohenstaufen king of Sicily, was to prove hostile to the Nicaean cause, invading Nicaea's Albanian coast in 1257 and allying with [[Michael II Komnenos Doukas]] against Nicaea in 1259, providing troops for the [[Battle of Pelagonia]].{{sfn|Angelov|2019|p=176}} After the Nicaean victory, [[Michael VIII Palaiologos]] attempted to marry the widowed Constance-Anna, who had remained at the Nicaean court during the reigns of her stepson and [[John IV Laskaris|stepgrandson]], in order to secure an alliance with Manfred. However, Constance-Anna refused and moved to her brother's court in Sicily in 1261, thus severing all ties with Byzantium and formally ending the alliance started by John III and Frederick II.{{sfn|Angelov|2019|p=226–227}}