The Gentlemen's Agreement address the issue of the immigration of Japanese workers into the United States. Japanese workers were constantly met with hostility when entering the US, especially in the city of San Francisco. President Teddy Roosevelt wanted to relieve these tensions, as he saw Japan as an ally against Russia expansion in the far east.
This is when Roosevelt uses his power as President to intervene. This agreement resulted in Japanese immigrants being unable to enter the US through other countries (like Canada). This allowed Japan to keep a large number of their workforce in their own country.