Charles V spent two decades demanding a general council of the church, on the reasoning that the German quarrel could be settled only by a body Protestants might accept and that the abuses they attacked were real and needed reform. Successive popes resisted, fearing a council would revive conciliar claims against papal authority and knowing the emperor wanted it held on German soil. Trent finally opened in 1545, in imperial territory but Italian-speaking, and it defined doctrine against the Reformers rather than negotiating with them, which was the opposite of what Charles had wanted from it, though its decrees on clerical residence and seminaries were the reform he had asked for.
A second religious argument of his reign concerned the Americas. Reports of the treatment of indigenous peoples by Spanish settlers, pressed above all by the Dominican Bartolome de las Casas, led Charles to promulgate the New Laws of 1542 restricting the encomienda system, and in 1550 to order a formal debate at Valladolid between Las Casas and the humanist Juan Gines de Sepulveda on whether the peoples of the Indies could justly be subjected by force. That a reigning emperor suspended conquests and convened a disputation on the legitimacy of his own empire is unusual enough to be worth recording, whatever the limited practical effect.
In 1556 he did something no emperor had done in living memory: he resigned. He divided his inheritance, giving Spain and the Netherlands to his son Philip and the imperial title to his brother Ferdinand, and retired to a house built beside the Hieronymite monastery of Yuste in Extremadura, where he lived with a small household, kept his clocks, and died in 1558.