[Sidenote: The wars with Henry of Trastamara.]
The wars were renewed from the side of Aragon, where Henry of Trastamara, who for years had been the Castilian monarch’s principal opponent, formed an alliance with the king of Aragon. The ruler of Aragon at that time was Pedro IV, a man of the type of Alfonso XI. Having overcome the seigniorial elements in his own realm he did not scruple to take advantage of Pedro I’s difficulties in the same regard to seek a profit for himself, or at least to damage a neighboring king of whom he felt suspicious. Prior to the outbreak of hostilities Pedro I gave himself up to a riot of assassinations, and among his victims were three of his half brothers and several members of their families. His enemies were not yet able to defeat him, however, even with the aid of Aragon, and a peace was signed in 1361. Shortly afterward, both Blanche of Bourbon and María de Padilla died, the latter deeply bemoaned by Pedro I. In 1363 Henry of Trastamara and Pedro IV again formed a league against the Castilian king, and it was at this time that Henry first set up a claim to the crown of Castile. To aid them in their project they employed the celebrated “White companies,” an army of military adventurers of all nations who sold their services to the highest bidder. They were at that time in southern France and (as usually happened in such cases) were regarded as unwelcome guests now that their aid was no longer required there. The pope (then resident at Avignon) gave them a vast sum of money on condition that they would go to Aragon, and Pedro IV offered them an equal amount and rights of pillage (other than in his own realm) if they would come. Therefore, led by a French knight, Bertrand du Guesclin, they entered Spain, and in 1366 procured the conquest of most of Castile for Henry, who had himself crowned king. Pedro I sought aid of his English neighbors, for England at that time possessed a great part of western France, and, in return for certain concessions which Pedro promised, Edward III of England was persuaded to give him an army under the command of the celebrated military leader, Edward, the Black Prince. It was Henry’s turn to be defeated, and he fled to France. Pedro I now took cruel vengeance on his enemies, disgusting the English leader, besides which he failed to keep the promises by which he had procured his aid. The English troops therefore went back to France, at a time when a fresh insurrection was about to break out in Castile, and when Henry of Trastamara was returning with a new army. Pedro I was utterly defeated at Montiel, and was besieged in a castle where he took refuge. Captured by Henry through a trick, he engaged in a hand-to-hand struggle with his half brother, and seemed to be winning, but with the aid of one of his partisans Henry at length got the upper hand and killed Pedro,--a fitting close to a violent reign.