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The steam locomotive allowed for the transportation of goods at a much more rapid rate than by horse. The railroad let people know exactly where and when goods would arrive. The trains also gave the cargo a safer ride as it was much more difficult to rob a train than a horse drawn transport. As more railroads were built, products could travel farther than ever before in a timely manner. This brought down the cost of freight transport and increased profits for many businesses.
Although this period has often been called the Era of Good Feelings due to its one-party dominance, in fact, Democratic-Republicans were deeply divided internally and a new political system was about to be created from the old Republican-Federalist competition that had been known as the First Party System.
This answer depends greatly on the time period in question, but generally speaking it is true that the presence of many rivers and mountains protected China from invaders, and allowed their culture to grow with little outside influence, with the exception of Mongolian invasions from the north.