First of all, make sure that your view doesn't contain the traffic from bots. To remove the robots traffic follow these steps:
- Go to the "Admin" upper tab
- Select your current property and view (or create a new view just to track non-robot traffic)
- Choose "View Settings"
- At "Bot Filtering", check the box : "Exclude all hits from known bots and spiders"
The changes are - if I remember well - not taken into account proactively, be aware of this!
Then, if you still have this direct traffic and want to investigate it there is several ways of doing it. I usually use the "Users Flow" to get a global overview of what they actually do and get an idea why they are there. An other way is to use the demographic tab, but for low traffic website it might be inaccurate and not give a lot of answers.
In all of the reports I mentioned, you can change the segment from "All Users" to "Direct Traffic" (click on it and search for the right segment).
Also, consider that some people use proxies located in the US for different purposes (avoid ads on some website, get access to specific content, etc.) and this could also be the cause of this traffic.