In the 1700s, the concept of individualism was so important for Americans that

In the 1700s, the concept of individualism was so important for Americans that rights were added to the Constitution in the Bill of Rights

Explanation:

The Mexican-American War, added new lands to America creating increase sectional tensions throughout the 1850s as a divide between or an imbalance of enslaved states.  

Explanation:

The main question became should slavery be allowed in newly acquired territory.  This issue of the expansion of slavery led to the divide of the North and the South (eventually the Civil War).