Detailed Instructions: In this task, you're given passages that contain mentions of names of people, places, or things. Some of these mentions refer to the same person, place, or thing. Your job is to write questions that evaluate one's understanding of such references. Good questions are expected to link pronouns (she, her, him, his, their, etc.) or other mentions to people, places, or things to which they may refer. Do not ask questions that can be answered correctly without understanding the paragraph or having multiple answers. Avoid questions that do not link phrases referring to the same entity. For each of your questions, the answer should be one or more phrases in the paragraph, and it should be unambiguous.
Q: Passage: As the 19th century progressed, the United States government's Indian removal policy pushed Native American tribes west of the Mississippi River. In 1830, the Indian Removal Act was signed into law, and though that act did not directly address the Potawatomi people of Indiana, it led to several additional treaties that resulted in their removal. In what came to be known as the Potawatomi Trail of Death, about 860 Potawatomi Indians who had refused to leave were forced to move from Indiana to Kansas. On September 14, 1838, the group camped near Williamsport, and on September 15 they camped in the southwestern part of the county before moving into Illinois. Before reaching their destination in Kansas, over 40 of them had died, many of them children; two children died and were buried at the second Warren County campsite.When the county was established, the Wabash River was vital to transportation and shipping. Zachariah Cicott traded up and down the river, and cities like Attica, Perrysville, Baltimore and Williamsport were founded near the river's banks and flourished because of it. In the 1840s, the Wabash and Erie Canal began to operate and provided even broader shipping opportunities, but the canal favored towns which were on the "right side" of the river; the canal was on the Fountain County side, and towns like Baltimore dwindled as a result. Some towns, such as Williamsport and Perrysville, managed to participate in canal traffic through the use of side-cuts that brought traffic from the canal across the river. When railroads were constructed starting in the 1850s, they in turn began to render the canals obsolete and allowed trade to reach towns that lacked water connections. The canal continued to be used through the early 1870s.
A:
What decade did the canals that provided broader shipping opportunities start to decline due to railroads?