Good art, needs sound.
This is great visually - your drawing skills are up to scratch, and you got things like the font right (which can often be a bad beginners' mistake). But this is really really lacking in one area.
IT NEEDS SOUND!
Without sound, the humour just goes right off. Add some background music definitely; I'd recommend putting something in that fits, rather than a piece of music that you personally like (ie. putting heavy metal or club techno into this just wouldn't ever work!). You might also want to consider voice acting, such as a narrator, or sound effects, like explosions going off in the Vietnam scene. This can be improved so easily, good luck.