The anti-immigrant Party was popular in Texas and successful in forcing the Democratic Party to become more fully organized in the state.

The missing word is know-nothing.

Explanation:

Know-nothing party, byname of American Party, U.S. political party that flourished in the 1850s. It was an outgrowth of the strong anti-immigrant and especially anti-Roman Catholic sentiment that started to manifest itself during the 1840s.

i dont believe in religion. lets all be peace

d. i assume the underlined word is "role." reformat if it isn't.

explanation:

role is closest to part because when replacing words, "playing a vital decision," "playing a vital activity," and "playing a vital dollar" don't make logical sense. the only meaningful choice is "playing a vital part."

this fits one of merriam-webster's definitions of role: "a function or part performed especially in a particular operation or process."