While Austin thought it would be advantageous some day for Texas to phase out of slavery, up until the Texas Revolution he worked to ensure that his colony's immigrants could bypass the Mexican government's resistance to it. Doing so ensured the population growth and economic development of his colony, which was primarily dependent on the monocropping of cotton and sugar. In August 1825, he recommended that the state government allow immigrants to bring their slaves with them through 1840, with the caveat that female grandchildren of the slaves would be freed by age 15 and males by age 25. His recommendation was rejected.