The most direct cause of the decline of the Spanish Crown's power is the conquest of the country by Napoleon and the attempted replacement of the Bourbon with the Bonapartes; the criollos sided with the Bonapartes, while the Peninsulares stuck with the Bourbon. Furthermore, the expansion of historically English colonies into the west would be limited by a PoD that eliminates the Peninsular War, since Napoleon wouldn't have been able to sell Louisiana after nicking it off the Spanish.