The heads of the Spanish colony in Guatemala even challenged him to put his theories into practice, saying that if he succeeded in subduing any tribes, they would admit that they had been unjust, and would abandon their opposition and liberate their slaves. This challenge Las Casas at once accepted, and selected for the field of his undertaking the mountains of the province of Tuzulatlan, inhabited by a warlike people, whom the Spaniards had never been able to conquer, partly on account of the difficult nature of the country, and partly on account of the skill and courage of the inhabitants in defending themselves. Besides the bare necessaries for his support, Las Casas only asked that the conditions expressed in the following agreement bearing the Governor’s signature should be scrupulously observed. The act was thus worded: “By these presents I promise and give my word in the name and on behalf of his Majesty and by the royal power which I hold that should you, or anyone of your religious here present, to wit, Fray Bartholomew de Las Casas, Fray Rodrigo de Ladrada, and Fray Pedro de Angulo, by your efforts and care, bring any provinces or Indians of them, which may be all or partly within my jurisdiction which I exercise for his Majesty, to peaceably recognise his Majesty as sovereign and to pay a tribute according as their means and property may permit either of gold, if it exists in their country, or of cotton, maize, or any other product which they possess and use for trade amongst themselves, I will, by virtue of his Majesty’s authority, recognise all such and their provinces in his Royal name and present them to his Majesty that they may serve him as his vassals; nor will I give them to any one, nor shall they be given in encomienda to any Spaniard either now or at any time. I will command that no Spaniard shall molest them nor enter their country, under grave penalties, for a period of five years, that they may not disturb them or hinder your preaching and their conversion, unless I should myself go personally when it may seem good to you and when you may accompany me; for in this matter I desire to fulfil the will of God and of his Majesty and to aid you as far as I possibly can to win the natives of this province to the knowledge of God and the service of his Majesty, etc.”