Major reason for a change in European attitudes toward imperialism after 1870

it became necessary for European industrialized nations to expand their markets globally in order to sell products that they could not sell domestically on the continent. ... The economic gains of the new imperialism were limited, however, because the new colonies were too poor to spend money on European goods.

Explanation:

i dont know but i found it on google

https://www.tamaqua.k12.pa.us/cms/lib07/PA01000119/Centricity/Domain/119/TheAgeofImperialism.pdf

a.tensions between the colonial elites and the backcountry men of virginia.

b. major john c. frémont led a rebellion called the bear flag revolt.

explanation:

during the bear flag revolt, from june to july 1846, a small group of american settlers in california rebelled against the mexican government and proclaimed california an independent republic. the republic was short-lived because soon after the bear flag was raised, the u.s. military began occupying california, which went on to join the union in 1850. the bear flag became the official state flag in 1911.