system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the difference between the Army and the Marines? (strategically and generally)

I have a friend in each one, I just don't fully understand the difference between the 2.
I have a pretty good understanding of the navy and the air force but I would love to hear some elaboration on this
thanks!
gpt
The Marines are an expeditionary force, more or less. Ready to go anywhere on short notice, bringing their own air support, logistics, etc, and also specializing in amphibious operations. 

The army is generally for larger and/or longer term jobs: take that area from a large opposing force, hold it, etc.  They have bigger logistical requirements generally, and rely on the USAF and/or USN for most of their fixed wing air support. 

The gist of it is that if you need an area secured immediately, you can use a Marine Expeditionary Unit (or certain specialized army units, like the 82nd airborne).