Just the term "Old West" conjures up images of outlaws on horseback. This image has largely been embellished by movies and pop-culture. However, like many such things, it is still grounded in some truth.
Throughout the latter part of the nineteenth century and even into the early twentieth century, the Western part of the United States hosted numerous outlaws and bandits. While local, state, and federal governments often did their best to stop their illegal activity, outlaws often found that they had the upper hand.
The main reason for this has simply to do with the sparsely populated nature of the American frontier. Towns and settlements were spread out, some being more than a day's ride from the next. Although the proliferation of the railroad and the telegraph helped, communication and travel were slow. A criminal could often commit a crime and vanish into the countryside before law-enforcement had any time to respond. Furthermore, there were seldom enough lawmen in the area to properly police it. Throughout this period, the country seemed to acquire territory faster than people could be recruited to populate it and defend it. Many locations resorted to posses and vigilante justice in their attempt to keep order. However, these unofficial crime-fighting groups were often ripe with corruption themselves. It was common for local peacekeepers to demand protection money from ranchers, farmers, and people passing through. At times, though, outlaws had the genuine support of the local population due to a shared mistrust of the government.
The vulnerability of the victims also played into the hands of outlaws. Pioneers and settlers heading west usually traveled with all their valuable belongings in tow. This made them ideal targets, and many bandits conducted regular raids on poorly defended wagon trains or attacked and robbed lone travelers.