The question seems to be asking which issue brought different regions of the United States together in support of a common cause during the War of 1812. While slavery and foreign policies were significant issues in the early 19th century, the most relevant point during the War of 1812 related to economic stability.
Different regions of the country, particularly those that were more economically dependent on trade (like the Northeast and parts of the South), had varying views on the war. However, the desire to stabilize the economy and deal with the impacts of British blockades and other trade issues related to the war created a semblance of unity, as many wanted to protect American economic interests.
So, the best answer in the context of the War of 1812 would be support of economic stability.