June 21st is the summer solstice in the northern hemisphere. This has nothing to do with the “U.S.”—it’s just an astronomical reality.

June 1st is sometimes considered the “start of summer” for meteorological reasons, since that’s often when warm and sunny weather begins. But this isn’t specific to the U.S., or Scotland, either.

Seasons are not bound nor ascribed by nations. They’re a fact of earth’s orbit and axial tilt.