New Industries in the Southwest of America and the Mexico Revolution was the reason for the Mexican to move in the 1920s.
Explanation:
Starting of new industries in the Southwest of America during the 1890s, especially in mining and agriculture, attracted Mexican migrant. The Mexican immigrants came from rural areas as labors to work in mining and agricultural fields for stability and employment. The Mexican Revolution increased the flow of Mexican people in America, who were refugees and political exile decamped to America to escape death and violence.
Because it's always only been about these 2 parties. Republican and democrat. The third parties are just there... they never ever get enough votes to win, electoral or popular vote.