Good, but could use work.
(SOME SPOILERS AHEAD)
Read the story now
The first issue is the grammar and punctuation. Granted, it's not all that pervasive in the story and only happens occasionally, but some of them are so glaring you have to take a moment to decipher what you're actually reading.
The second issue is the characters. Other than John and Lieutenant Casey, none of the characters really have any individual traits or importance to the story. Granted, giving a name and a major role to every group member would be impossible, but make the major cast a little bit longer. There's also the issue of everyone except one person making it across the border. There's hardly any loss or sacrifice on the journey, which in a real scenario would cause some serious internal dilemmas with John's group. Showing the group bickering and fighting at times instead of showing them following John without a single protest would actually make the story a lot less black and white.
My only other issue is Casey's story. He's actually a very well-developed character, and I kept on reading excited to see what went on in his head. But having him betray the group the first chance he gets and then stay in America makes his entire arch seem a bit pointless, since it really just goes nowhere.
That being said, the story is indeed compelling, and the premise is excellent. My advice to the author would be to add a bit more depth to some of the side characters, proofread (or have a friend do it) to sniff out any grammar errors, and try not to make the story so clear-cut (John's group stays together far too easily in this story). Overall, I liked it, but I think the author should consider revisiting this story after a bit more experience in writing.