Manifest destiny and slavery on acquired territories (specially Texas) motivated such conquest.
See related questions.
Racism was abolished partially in the 1930's when the slavery famine began to die down but there is still lots of racism going on today!
Racism played a significant role in the justification and perpetuation of slavery, as it was used to dehumanize and justify the mistreatment of enslaved individuals based on their race. The belief in the inherent superiority of certain races fueled the practice of slavery and helped maintain systems of oppression.
In one single word: racism Please see related questions.
There isn't much racism because it's always the same color, although there is some racism on Americans because Mexicans want to go to USA to work and earn money and USA doesn't let them.=(
It was the belief at the time. It however, was pushed by xenophobia, racism and of course, pro-slavery interests.
Since ever. Even before the conquest of the Americas by European settlers, many Native American civilizations practiced conquest and slavery of less advanced peoples. Some cultures (Mayans, Aztecs) even practiced human sacrifice with their conquered enemies.
institutional racism causes interpersonal racism.
Prejudice, Racism
Racism aside, the most well known icon of dirtiness in Mexico is a character living in the streets of Mexico City known as 'El Changoleon'. Please see related links for a picture.
Racism in the 1930s manifested in discriminatory practices, segregation, and violence against African Americans, Hispanic Americans, Asian Americans, and other minority groups. The Great Depression exacerbated racial tensions as economic hardship fueled competition for jobs and resources, leading to increased discrimination and inequalities. The 1930s also saw the rise of white supremacist groups like the Ku Klux Klan, further perpetuating racist ideologies and actions.
Racism
interpersonal racism