system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Given that America has one of the most powerful armies. Why don't they use that power to stomp out Mexican cartels and the gang problems in and around the USA?

Like instead of using the money to go to war. We'd use it for that sort of thing.

Thanks for the responses guys! Learned some interesting stuff.
gpt
The first one would mean the US is invading Mexico.  You can't just take an army and go into another country and blow shit up and kill people.  Mexico has their own police that should do that, and they partner with Americans and get support from Americans all the time.  

Similar thing with the second situation.  States have their own police force to combat gang violence.  The National Guard cannot go into a US state and enforce laws unless Martial Law is declared.