President JamesPolk during Westward expansionJames SHriber
James K. Polk was the most significant on the country during westward expansion because got the Oregon territory from Britain as a 'treaty', annexed Texas, and got California so he fulfilled westward expansion.
These expansions happened in the 1840's, they happened because Polk wanted to fulfill westward expansion and thats exactly what he did, other things that were happening at the time were The Mexican American war which lasted from 1840-1849.
This affected people directly by encouraging them to move west. It affected the country because it increased its size. it affected the North and South because now the abolitionists and the people who wanted slaves were sort of uneven based on land.
This significantly affected westward expansion because it literally expanded all the way west.