Final answer:
The favorable climate and vast open grasslands of Texas geography were essential for the development of the cattle kingdom economy, as they provided optimal conditions for cattle breeding, grazing, and transportation to eastern markets via the railroad.
Step-by-step explanation:
The geography of Texas significantly aided the development of the cattle kingdom economy primarily because of the favorable climate for cattle breeding and grazing. Texas boasts vast, dry flatlands with grassy expanses well-suited to the demands of cattle ranching. Additionally, with less than 20 inches of rain per year in certain regions and its sprawling open terrain, crops are often less profitable, making cattle ranching a common agricultural alternative. The adaptation of cattle ranching to these geographical conditions led to a thriving cattle industry that, when coupled with the advent of the transcontinental railroad, created efficient ways to transport cattle to eastern markets for sale, thus booming the economy.