You might run into trouble with plane radar systems. Here we have built-in features that disables certain frequencies when the router notices such activity.
In the worst case, you will get a visit by the FCC and they confiscate your device. And they will send you an invoice for their trouble.
As long as you configure channels you are allowed to use in the US it shouldn't be a problem. Otherwise you might have issues with some clients not being able to connect to your wifi.
Depends where it comes from. The vendor should have a data sheet saying what frequencies are available in which regions. You will then have to disable the frequencies not permitted in your country. Or flash a local firmware onto the device.
Most routers have a WiFi region setting to deal with that sort of stuff, but if it doesn't look up what channels are allowed in the US and manually set it to use those.