There are a few ways you could accomplish this. First would be to make a layer mask in the shape of the country you're designing for, and the second may be layer blending styles.
I have some experience with Photoshop, but my specialty is 3d modeling, so I'd need to play with this a little to get it right.
An easy way to make a layer mask would be to either use your magic wand tool, and convert your selection to a mask, or, if your country design is on a clear background, just hold CTRL and click on your layer to select only opaque pixels, and again, convert your selection to a mask.
Those would be non-destructive ways of doing it.
Others with more Photoshop experience may be able to tell you a better way.
