Which of the following was a focus of the new republican party?
supporting irish catholic immigration
encouraging the use of popular sovereignty to determine where slavery could exist
promoting states’ rights
halting the spread of slavery

A focus of the new Republican Party was halting the spread of slavery.

Explanation:

The Republican Party was formed in 1854 by former members of the Whig Party, the Free Soil Party, and some abolitionist Democrats. What all these groups had in common to form the new party was their ideological belonging to the powerful anti-slavery movement, which brought together all white-skinned people in the Northern States of the United States who were fighting to abolish slavery of black people in the southern states of the North American country. They also agreed to promote an economic policy based on two fundamental aspects: a protectionist trade policy, which would diminish or impede imports through high tariffs, to protect the domestic industry from foreign competition; and a policy of "federal improvements", by which the Federal Government had to invest much more money in public works or infrastructure (bridges, roads, etc.) to stimulate the economy.

"the royal proclamation of 1763"