In order to maintain the two great political parties as vital bonds of national unity, early-nineteenth-century politicians

Slavery

Explanation:

Early nineteenth century politicians avoided any public discussions about the issue of slavery owing mainly to the fact that an issue like slavery could cause a national disorder if two sections of the nation had an argument about it. They preferred to remain silent on the issue of slavery, and did not bring it up as a means of gaining favour from the black population. During the 1848 presidential elections in the United states, both the Democrats and the other party did not involve themselves in any discussions related to or concerning slavery. This was a way of maintain national unity.

agriculture revolution