The second sentence is more common as it covers anything that is special. The first is fine, but usually means something that some people might fine a little strange. Hope this helps, Zhou! :)

Unique means one of a kind; unlike anything else. Peculiar, in your sentence, means relating to or belonging to. Both sentences suggest that the problem can be found in countries other than America. I would personally prefer to use peculiar. Peculiar also has another meaning, which is strange or unusual.

Peculiar is more like "odd" and unique is used in a more positive way like "special."

Both sentences are correct and mean the same thing. When writing and speaking, "unique to" is a better choice nowadays "Peculiar to" is old-fashioned and a little "literary." In fact, as you can see from other answers here, not all native speakers are familiar with this old phrase and its meaning. The word "peculiar" by itself usually means strange, unusual, weird, bizarre, or odd. The English word "crwth" is peculiar because it doesn't contain any of the normal vowels. John Cage's piece of music, "4'33," is peculiar because it consists of complete silence. Airplanes with pusher propellers look peculiar because we are used to seeing the propellers in front. However, in the phrase "peculiar to," it "peculiar" loses the connotation of being weird or odd. I think that "unique to" and "peculiar to" are interchangeable.

Hello, Peculiar means different to what is normal or expected; strange. Unique means being the only one of its kind; unlike anything else. I hope this answers your question. If you’d like to practice speaking. I’d be happy to help you develop a study plan. Feel free to view my teaching profile and class offerings and send me a message if you think I can help you. Regards.