The authorities want the cheap labor and the profits they generate for the wealthy few. The migrants refuse to take any steps towards assimilation, insisting on speaking their own language. Too many migrants arriving too fast cause a glut in the labor pool, even for the most menial of jobs. Thousands of migrants are unemployed and seek the benefits of the host country's social welfare system. Robberies and burglaries rise.
Violent crimes rise.
The youngest migrants form into small gangs. They import illegal drugs. The locals snap. There is a riot. They are accused of racism and zenophobia.