1870s: Several people are killed in the United States' first national railroad strike, which threatens to damage the nation's trade. The strike is caused by a 10 percent wage cut in railroad employees' pay, the second such cut in four years.

Today: After terrorists use three commercial airplanes to attack the World Trade Center and the Pentagon, nationwide travel comes to a halt. Although people slowly begin to travel again a few months after the attacks, the tragic events help to plunge the nation into an economic recession. The transportation sector is one of the hardest hit.

1870s: Medicine is largely undeveloped and shortsighted, and medical education is not yet regulated. As a result, people must take precautions against getting sick. This includes staying out of the cold as much as possible, for even an hour out in the elements is enough to contract an...