Final answer:
The new party system began in the early 1850s following the decline of the Whigs post-1852 election, notably marked by the rise of the Republican Party in 1856.
Step-by-step explanation:
The new party system, generally considered the beginning of the third party system, started in the early 1850s. This shift occurred after the election of 1852, where the Whigs began to decline, and new parties such as the Know-Nothing Party and the Republican Party emerged. The Republican Party's significant rise in 1856, where they garnered substantial support from the North, marked the definitive start of a new party system. This shift was primarily due to increasing tensions over issues such as the annexation of Cuba, the spread of slavery into Kansas, and the enforcement of the Fugitive Slave Law, which led to a divide between the North and the South.