Prosperity.

At the start of the 1850s, a tide of prosperity buoyed the U.S. economy. The discovery of gold in California in 1848 generated dramatic developments and windfall earnings. Moreover, a few years later, the outbreak of the Crimean War created strong European demand for American wheat, a demand nicely timed with the opening of the railroad and rapid cultivation of the Midwest. During the 1850s American farmers exported some $420 million worth of wheat, mainly to European markets. Meanwhile, immigrants continued to pour into the country, looking for work or to buy land or both. These developments drew European investors back to American investments (which had become suspect after several American states had repudiated their debts in the late 1830s). These sources of capital played a prominent role in financing the 1850s boom in railroad construction: European investors fed close to $200 million in capital...