What was a major consequence of United States expansionism in the first half of the nineteenth century?

A. Increased sectional discord accompanied by the growing failure of compromise.
B. The need for a strong military to protect the newly gained territory.
C. The increased concentration of the slave population along the Atlantic seaboard.
D. Large overseas markets for goods manufactured in New England.
E. Increased popular support for the Whig Party.

A. Increased sectional discord accompanied by the growing failure of compromise.

Explanation:

The incorporation of new territories brought the positive result of the enlargement of the country´s territory, which meant new lands and economic opportunities.

But at the same time, it created new legal, social and political challenges.  The most contentious issue of American politics until the Civil War was slavery. The country got divided along this line. There were slave states and free states. Government and politicians strove to strike a weak, precarious balance in Congress for several decades. So, there were always discussions and confrontation among factions and parties on whether new states carved out from the newly acquired territories were to be admitted in the Union as free states or slave states.  

the answer is c my brotha. c.   formed an alliance with the soviet union.