Question

Mexico and the United States have strained border relations mainly due to the following factor:

Answer 1

Assuming that this is referring to the same list of options that was posted before with this question, the correct response would be "drug trafficking", since the US is upset that a large amount of drugs come from over the Mexican border. 

Answer 2

I don’t know how it got a green check that’s so wrong and I feel bad for y’all.

It’s Mexico is the largest foreign supplier of marijuana and methamphetamine to the US market