Final answer:
The internal improvement championed during the 1850s was the Transcontinental Railroad, a critical component in enhancing internal development, trade, and American expansion.
Step-by-step explanation:
The 'internal improvement' championed during the 1850s referenced in this question is the Transcontinental Railroad. This period was marked by the significant growth of infrastructure, with the expansion of railroad lines and telegraph systems accounting for a major transformation in American transportation and communication networks. The railroads, in particular, were a major component of internal improvements as they connected port cities with the interior, thereby enhancing internal development, facilitating trade, and spreading American influence.