Final answer:
Cattle trails began in South Texas due to the availability of millions of longhorn cattle following the clearance of bison and the expansion of the rail system to Missouri, which enabled profitable transport of beef to Eastern markets.
Step-by-step explanation:
The cattle trails tended to begin in South Texas because by the 1860s, this area was home to millions of longhorn cattle after being cleared of bison. With the completion of the nation's rail system extending to western Missouri and the ability to transport beef efficiently to urban markets, ranchers initiated cattle drives to the nearest rail terminus.
These cattle drives played a significant role in western expansion and helped ranchers capitalize on the demand for beef in eastern markets, facilitating the growth of cow towns and altering the West's economy and society.
As the cattle industry developed, it faced challenges such as cattle fever and conflicts over land resources and infrastructure like fences. Nevertheless, the cattle drives and sales of longhorn steers transformed the West, creating an era of cowboys and cattle drives that is a defining aspect of American history.