Why many American presidents and foreign monarchs are also eligible to inherit the British throne

1. Because the British royal family implements the primogeniture system.

The throne should first be inherited by the eldest son of the current monarch, then by the other sons in order, and finally by the daughter.

2. The tradition of primogeniture gives the descendants of the eldest son, regardless of seniority, priority over the succession order of the second son.

Although the daughter of the eldest son has lower priority than her brothers, she is higher than her uncles and aunts, and even though her children have foreign surnames, they are treated equally by the royal family in terms of blood.