entities.cs

public class Country
{
        public int Id { get; set; }
        public string Name { get; set; }
        public List<State> States { get; set; }
}
    
public class State
{
        public int Id { get; set; }
        public string Name { get; set; }
        public int CountryId { get; set; }
        public Country Country { get; set; }
}
    
public class Person
{
        public int Id { get; set; }
        [Required]
        public string Name { get; set; }
        public string Biography { get; set; }
        [Range(1, int.MaxValue, ErrorMessage = "You must select a state")]
        public int StateId { get; set; }
        public State State { get; set; }
}