Answer:
Historically, immigrants have immigrated into lower-paying jobs/lower-skilled jobs(Due to job requirement restrictions, judgement, and a lack of education in specific skills). Due to this increase in the amount of people who can fulfil these low-paying/low-skilled jobs, the wages of these workers decrease since there are so many people who can do the work. A good comparison of this can be seen in the cost of something like salt and sugar for instance. A thousand years ago, these would be extremely expensive since they are so rare to obtain. Nowadays, however, salt and sugar is extremely cheap, since it can be obtained and produced with ease.
Hope this helps!