#The books are set in Britain, so they focus on British events.
The books are set in Britain, so they focus on British events.
- Founding of Hogwarts
Founding of Hogwarts
This is the British school. There is an American school too - Ilvermorny. However, remember that Hogwarts was founded around the year 1000. The Americas weren't colonized then - the world was very different.
- Grindelwald and Dumbledore
Grindelwald and Dumbledore
This also took place in the Americas - Fantastic Beasts and Where to Find Them has Grindelwald and Dumbledore as some central plot points - not going into detail for spoilers.
- Tom Riddle
Tom Riddle
Well yes... He was British, so the British had to take care of him. The Americas have most likely had their share of Dark Wizards too.
Conclusion
The books focus on Britain because J. K. Rowling is British; and other things do happen in the other parts of the world, we just don't see them because it's set in Britain. The books focus on Britain because J. K. Rowling is British; and other things do happen in the other parts of the world, we just don't see them because it's set in Britain.