The efforts of Bavaria’s Wittelsbach dukes to increase their power and to give unity to the duchy had met with a fair measure of success.

Now, however, Louis II and Henry XIII, the sons of Duke Otto II, who for two years after their father's death have ruled Bavaria jointly, split their inheritance: …

...Louis II obtains the western part of the duchy, afterwards called Upper Bavaria; he also receives the Electoral Palatinate.

Henry secures eastern or Lower Bavaria.

Bavaria’s partitioning and repartitioning among different members of the family will for the next two hundred and fifty years bring intermittent warfare and attendant weakness.

The future Duke Louis II of Bavaria, born in Heidelberg, is a son of duke Otto II and Agnes of Palatinate; she is a daughter of the Welf Henry V, Count Palatine of the Rhine, her grandfathers were Henry XII the Lion and Conrad of Hohenstaufen.

Louis had supported his brother-in-law king Conrad IV of Germany against Henry Raspe in 1246, and in 1251  was at war again against the bishop of Regensburg.

Louis had in 1253 succeeded his father as duke of Bavaria.

When, two years later, the Wittelsbach country is divided among Otto's sons, Louis receives the Palatinate.

Louis, in Donauwörth in 1256, orders the execution of his wife Marie of Brabant—a daughter of Henry II, Duke of Brabant and Marie of Hohenstaufen—due to mistaken suspicion of adultery, although any actual guilt on her part could never be validated.

As expiation, Louis founds a Cistercian friary, Fürstenfeld Abbey (Fürstenfeldbruck), near Munich.

Louis supports Richard of Cornwall during the German interregnum that follows King William's death in 1256.

The partition of the Wittelsbach lands, being against Imperial law, causes the anger of the bishops in Bavaria, who ally themselves with King Ottakar II of Bohemia.

Ottokar invades Bavaria in August 1257, but Dukes Louis and Henry, in one of the rare harmonious actions of the two brothers, who often argue, manage to repulse the attack.

Conradin, son of the late Holy Roman Emperor Conrad IV, had assumed the title of King of Jerusalem and Sicily and had taken possession of the Duchy of Swabia in 1262, remaining for some time in his duchy.

Conradin's first invitation to Italy had come from the Guelphs of Florence: they had asked him to take arms against his father's half-brother Manfred, who had been crowned king of Sicily in 1258 on a false rumor of Conradin's death.

Conradin’s uncle and guardian, Louis II, Duke of Upper Bavaria, had refused this invitation on his nephew's behalf.

After Charles I of Anjou had defeated and killed Manfred at Benevento, taking possession of southern Italy, envoys from the Ghibelline cities had then gone to Bavaria and urged Conradin to come and free Italy.

Count Guido de Montefeltro, representing Henry of Castile, Senator of Rome, has offered him the support of the eternal city.

Pledging his lands, Conradin crosses the Alps and issues a manifesto at Verona setting forth his claim on Sicily.

Conradin’s cause seems to prosper, notwithstanding the defection of his uncle Louis and of other companions who have returned to Germany, the threats of Clement IV, and a lack of funds.

Proclaiming him King of Sicily, his partisans, among them Prince Henry of Castile, both in the north and south of Italy have taken up arms; Rome receives his envoy with enthusiasm; and the young king himself receives welcomes at Pavia, Pisa and Siena.

Prince Frederick of Castile, unhappy under the rule of his elder brother Alfonso, he may have participated in the rebellion of his brother Henry in 1255; in any case, he had been exiled from Castile in 1260 and joined Henry as a knight errant in Tunis serving under Sultan Al Mustansir against his enemies.

H later joined the service of King Manfred of Sicily, and in 1266 fought at the Battle of Benevento.

He escaped the defeat there and returned to Tunis.

The anti-Angevin revolt in Sicily in 1267 provides an opportunity for him to cross over again: his Spanish fleet, carrying also a number of knights from Pisa, and Spanish knights soldiering from Tunis, disembarks in the Sicilian city of Sciacca in September 1267, and most of the island rebels against the Angevin rule while Henry (now Senator of Rome) also declares for Conradin in Rome.

Only Palermo and Messina remain loyal to Charles.

The revolt spreads to Calabria and Apulia.

The Church had excommunicated Conradin in November of 1267, but his fleet had won a victory over that of Charles; and in July 1268, Conradin himself enters with immense enthusiasm in Rome.

Conradin, having strengthened his forces, marches towards Lucera to join the Saracen troops settled there since the time of his grandfather.

On August 23, 1268, his multinational army of Italian, Spanish, Roman, Arab and German troops encounters that of Charles at Tagliacozzo, in a hilly area of central Italy.

The eagerness of Conradin's Spanish knights under Infante Henry of Castile in the most successful first charge, and the error in obtaining plunder in the enemy's camp after that momentary victorious assault, gives the final victory to the reinforced French.