Spanish settlers first established cattle ranching in Texas in the 1700s, driving herds of longhorn cattle north from Mexico to supply missions along the Rio Grande and San Antonio Rivers. By the 1800s, Tejano ranchers had established cattle ranching as the primary economic activity in Texas, driving longhorn cattle to markets in New Orleans and other states. However, problems with rustlers and limited access to markets kept the cattle industry in Texas relatively small until after the Civil War, when Union blockades during the war prevented Texas longhorns from being driven out of state, allowing their numbers to grow substantially.