Answer:
The Democratic Party was the result of the split that occurred inside the Democratic-Republican Party, established by Thomas Jefferson and James Madison in the early 1790´s, due to big differences in viewpoints on: slavery, equality and also the role of a centralized government over the power of individual states.
The Democratic Party thus, was born from the factions that broke off from the original Democractic-Republicans after the elections of 1824 and who followed the ideals of Andrew Jackson, especially on slavery and government involvement in all aspects of American life. Originally, this party had three tenets over which they were unified: slavery, individual rights and state sovereignity. In essence, they said they were the party of "the common man".
However, after a good period of unity, and constant successes against the then opposing party, the Whig Party, differences began to emerge between the Democrat members of the North and those of the South, especially on the issue of slavery, and allowing this institution to spread to newly acquired lands. The crisis initiated in the 1850´s, when the issue of slavery began to rip the party appart into Northern and Southern factions. Democrats from the North were not open to negotiation of certain aspects with those of the South and the division happened. Thus, a group of Democrats, the War Democrats and the Copperheads.
The result of this split was not only the emergence of different groups, especially of those who, although Democrats, did not believe in any form of slavery, but also, the allowance of time, and space for the Whig Party to reorganize its efforts and become the Republican Party. This is the reason why Repubicans were able to reconquer the presidency with Abraham Lincoln, and why so many of the issues that Democrats opposed were able to take form as policies in the U.S.
